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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    Form 13F

                               Form 13F COVER PAGE


Report for the Calendar Year or Quarter Ended:  March 31, 2005
                                                --------------

Check here if Amendment [ ]; Amendment Number:              
                                                  ------------
  This Amendment (Check only one.): [ ]  is a restatement.
                                    [ ]  adds new holdings entries.


Institutional Investment Manager Filing this Report:

Name:     Hennessy Advisors, Inc.
Address:  The Courtyard Square
          750 Grant Avenue, Suite 100
          Novato, CA  94945

Form 13F File Number:  028-06715

The institutional investment manager filing this report and the person by whom
it is signed hereby represent that the person signing the report is authorized
to submit it, that all information contained herein is true, correct and
complete, and that it is understood that all required items, statements,
schedules, lists, and tables, are considered integral parts of this form.

Person Signing this Report on Behalf of Reporting Manager:

Name:     Teresa M. Nilsen
Title:    Executive Vice President and Chief Financial Officer
Phone:    (415) 899-1555

Signature, Place, and Date of Signing:


/s/ Teresa M. Nilsen                  Novato, CA                   April 8, 2005
--------------------------------------------------------------------------------
Teresa M. Nilsen                      City, State                      Date


Report Type  (Check only one):

[X]  13F HOLDINGS REPORT. (Check here if all holdings of this reporting manager
     are reported in this report.)

[ ]  13F NOTICE. (Check here if no holdings reported are in this report, and all
     holdings are reported by other reporting manager(s).)

[ ]  13F COMBINATION REPORT. (Check here if a portion of the holdings for this
     reporting manager are reported in this report and a portion are reported by
     other reporting manager(s).)






                              FORM 13F SUMMARY PAGE



Report Summary:


Number of Other Included Managers:                              0
                                                 ----------------------

Form 13F Information Table Entry Total:                       137
                                                 ----------------------

Form 13F Information Table Value Total:                $1,340,526
                                                 ----------------------
                                                       (thousands)



List of Other Included Managers:  NONE







Page 1 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
AEGON NV ORD REG AMER      ADR       007924103       137     10,147 SH       SOLE                                  0          10,147

AETNA INC                 COMMON     00817Y108    22,935    306,000 SH       SOLE                            306,000               0

AK STEEL HOLDING CORP     COMMON     001547108    14,587  1,318,900 SH       SOLE                          1,318,900               0

ALBERTSONS INC            COMMON     013104104     3,413    165,300 SH       SOLE                            165,300               0

ALLEGHENY ENERGY INC      COMMON     017361106     2,104    101,846 SH       SOLE                            101,500             346

ALLIANCE IMAGING INC      COMMON     018606202    16,201  1,696,400 SH       SOLE                          1,696,400               0

ALLTEL CORP               COMMON     020039103     3,660     66,730 SH       SOLE                             65,900             830

ALTRIA GROUP INC          COMMON     02209S103    13,602    208,012 SH       SOLE                            206,825           1,187

AMERADA HESS CORP         COMMON     023551104     1,770     18,400 SH       SOLE                             18,400               0

AMERIGROUP CORP           COMMON     03073T102    18,445    504,500 SH       SOLE                            504,500               0

AON CORP                  COMMON     037389103     3,878    169,800 SH       SOLE                            169,800               0

ASHLAND INC               COMMON     044204105     1,950     28,900 SH       SOLE                             28,900               0

AT&T CORP                 COMMON     001957505     9,054    482,889 SH       SOLE                            481,500           1,389

BANK of AMERICA CORP      COMMON     060505104     4,478    101,536 SH       SOLE                             85,200          16,336

BB&T CORP                 COMMON     054937107     3,576     91,500 SH       SOLE                             91,500               0

BELLSOUTH CORP            COMMON     079860102     3,676    139,840 SH       SOLE                            135,900           3,940

BLACK & DECKER CORP       COMMON     091797100    18,744    237,300 SH       SOLE                            237,300               0

BLOUNT INTL INC           COMMON     095180105    18,602  1,095,500 SH       SOLE                          1,095,500               0

BLUEGREEN CORP            COMMON     096231105    12,367    962,400 SH       SOLE                            962,400               0

BP PLC  -ADS               ADR       055622104     4,529     72,588 SH       SOLE                             66,100           6,488

BRINKS CO                 COMMON     109696104    16,708    482,900 SH       SOLE                            482,900               0






Page 2 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
BRISTOL MYERS SQUIBB      COMMON     110122108     4,109    161,400 SH       SOLE                            160,600             800

BRUNSWICK CORP            COMMON     117043109     1,729     36,900 SH       SOLE                             36,900               0

BUILDING MATERIALS 
  HLDG CP                 COMMON     120113105    22,169    498,400 SH       SOLE                            498,400               0

BUNGE LTD                 COMMON       sedol      18,039    334,800 SH       SOLE                            334,800               0
                                      2788713

C B RICHARD ELLIS SVCS    COMMON     12489L108       350     10,000 SH       SOLE                                  0          10,000

CARPENTER TECHNOLOGY 
  CORP                    COMMON     144285103    19,391    326,400 SH       SOLE                            326,400               0

CEMEX S A  -ADR            ADR       151290889     4,169    115,000 SH       SOLE                            115,000               0

CENTENE CORP              COMMON     15135B101    20,189    673,200 SH       SOLE                            673,200               0

CHAMPION ENTERPRISES 
  INC                     COMMON     158496109    15,177  1,614,600 SH       SOLE                          1,614,600               0

CHARLES SCHWAB CORP       COMMON     808513105       106     10,100 SH       SOLE                                  0          10,100

CHEVRONTEXACO CORP        COMMON     166764100     5,372     92,130 SH       SOLE                             73,600          18,530

CIRCUIT CITY STORES INC   COMMON     172737108     1,735    108,100 SH       SOLE                            108,100               0

CITIGROUP INC             COMMON     172967101    11,229    249,877 SH       SOLE                            248,600           1,277

CLEVELAND-CLIFFS INC      COMMON     185896107    26,780    367,500 SH       SOLE                            367,500               0

COCA-COLA COMPANY         COMMON     191216100     1,575     37,800 SH       SOLE                             36,700           1,100

COMMERCIAL METALS         COMMON     201723103    25,584    754,900 SH       SOLE                            754,900               0

CONAGRA FOODS INC         COMMON     205887102     3,802    140,700 SH       SOLE                            140,700               0

CONSOL ENERGY INC         COMMON     20854P109    21,860    464,900 SH       SOLE                            464,900               0

DICKS SPORTING 
  GOODS INC               COMMON     253393102     1,657     45,100 SH       SOLE                             45,100               0

DONNELLEY (R R) & 
  SONS CO                 COMMON     257867101     3,595    113,700 SH       SOLE                            113,700               0

DOW CHEMICAL              COMMON     260543103     3,973     79,700 SH       SOLE                             79,700               0






Page 3 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
DU PONT (E I) DE 
  NEMOURS                 COMMON     263534109    13,228    258,160 SH       SOLE                            256,575           1,585

ELECTRONICS BOUTIQUE 
  HLDG CP                 COMMON     286045109    19,096    444,400 SH       SOLE                            444,400               0

EMERSON ELECTRIC          COMMON     291011104     1,334     20,550 SH       SOLE                                  0          20,550

ENRON CORP                 ADR       293561106         0     10,392 SH       SOLE                                  0          10,392

EXXON MOBIL CORPORATION   COMMON     30231G102     9,116    152,949 SH       SOLE                            143,750           9,199

FANNIE MAE                COMMON     313586109     3,022     55,500 SH       SOLE                             55,500               0

FMC TECHNOLOGIES INC      COMMON     30249U101     1,606     48,400 SH       SOLE                             48,400               0

FORD MOTOR CO             COMMON     345370860     3,098    273,446 SH       SOLE                            272,800             646

GENERAL ELECTRIC CO.      COMMON     369604103     7,680    212,989 SH       SOLE                            206,325           6,664

GENERAL MILLS INC         COMMON     370334104     3,957     80,500 SH       SOLE                             80,500               0

GENERAL MOTORS CORP       COMMON     370442105     8,351    284,135 SH       SOLE                            282,000           2,135

GENESCO INC               COMMON     371532102    17,419    612,900 SH       SOLE                            612,900               0

GEORGIA GULF CORP         COMMON     373200203    17,620    383,200 SH       SOLE                            383,200               0

GOODYEAR TIRE & 
  RUBBER CO               COMMON     382550101     1,957    146,600 SH       SOLE                            146,600               0

GRACE (W R) & CO          COMMON     38388F108    11,947  1,402,200 SH       SOLE                          1,402,200               0

GREENBRIER COMPANIES 
  INC                     COMMON     393657101    19,784    563,800 SH       SOLE                            563,800               0

HARRIS CORP               COMMON     413875105     1,933     59,200 SH       SOLE                             59,200               0

HEINZ (H J) CO            COMMON     423074103     3,765    102,200 SH       SOLE                            102,200               0

HENNESSY ADVISORS INC     COMMON     425885100    35,800  1,476,297 SH       SOLE                                  0       1,476,297

HEXCEL CORP               COMMON     428291108    20,414  1,316,200 SH       SOLE                          1,316,200               0

HSBC HOLDINGS PLC          ADR       404280406     3,668     46,200 SH       SOLE                             46,200               0






Page 4 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
HUGHES SUPPLY INC         COMMON     444482103     1,550     52,100 SH       SOLE                             52,100               0

HUNT (JB) TRANSPRT 
  SVCS INC                COMMON     445658107    18,624    425,500 SH       SOLE                            425,500               0

INTL PAPER CO             COMMON     460146103     3,842    104,425 SH       SOLE                            103,550             875

IPSCO INC                  ADR       462622101    20,364    399,300 SH       SOLE                            399,300               0

J P MORGAN CHASE & CO     COMMON     46625H100    10,582    305,845 SH       SOLE                            303,800           2,045

JONES LANG LASALLE INC    COMMON     48020Q107    23,796    510,100 SH       SOLE                            510,100               0

JOY GLOBAL INC            COMMON     481165108     2,563     73,100 SH       SOLE                             73,100               0

KERR-MCGEE CORP           COMMON     492386107     5,193     66,300 SH       SOLE                             66,300               0

KIMBERLY-CLARK CORP       COMMON     494368103     4,031     61,326 SH       SOLE                             60,200           1,126

LANDSTAR SYSTEM INC       COMMON     515098101    16,974    518,300 SH       SOLE                            518,300               0

LILLY (ELI) & CO          COMMON     532457108     3,569     68,500 SH       SOLE                             68,500               0

LINCOLN NATIONAL CORP     COMMON     534187109     3,697     81,900 SH       SOLE                             81,900               0

LONE STAR TECHNOLOGIES    COMMON     542312103     1,766     44,800 SH       SOLE                             44,800               0

LYONDELL CHEMICAL CO      COMMON     552078107    20,588    737,400 SH       SOLE                            737,400               0

MARATHON OIL CORP         COMMON     565849106     4,950    105,500 SH       SOLE                            105,500               0

MARSH & MCLENNAN COS      COMMON     571748102     3,772    124,000 SH       SOLE                            124,000               0

MASSEY ENERGY CO          COMMON     576206106     2,226     55,600 SH       SOLE                             55,600               0

MAVERICK TUBE CORP        COMMON     577914104     1,736     53,400 SH       SOLE                             53,400               0

MAY DEPARTMENT 
  STORES CO               COMMON     577778103     5,046    136,300 SH       SOLE                            136,300               0

MCDERMOTT INTL INC        COMMON     580037109    19,676  1,039,400 SH       SOLE                          1,039,400               0

MEADWESTVACO CORP         COMMON     583334107     3,790    119,100 SH       SOLE                            119,100               0






Page 5 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
MERCK & CO                COMMON     589331107    10,274    317,406 SH       SOLE                            315,300           2,106

MERITAGE HOMES CORP       COMMON     59001A102    19,956    338,700 SH       SOLE                            338,700               0

MOLINA HEALTHCARE INC     COMMON     60855R100    18,966    411,500 SH       SOLE                            411,500               0

NATIONAL CITY CORP        COMMON     635405103     3,531    105,400 SH       SOLE                            105,400               0

NCR CORP                  COMMON     62886E108    18,602    551,332 SH       SOLE                            551,300              32

NOVA CHEMICALS CORP        ADR       66977W109    17,330    403,500 SH       SOLE                            403,500               0

NOVAMERICAN STEEL INC      ADR       669959108    17,032    339,900 SH       SOLE                            339,900               0

NUCOR CORP                COMMON     670346105    23,036    400,200 SH       SOLE                            400,200               0

NVR INC                   COMMON     62944T105    19,468     24,800 SH       SOLE                             24,800               0

OLD DOMINION FREIGHT      COMMON     679580100    17,083    548,400 SH       SOLE                            548,400               0

OREGON STEEL MILLS INC    COMMON     686079104    21,634    940,600 SH       SOLE                            940,600               0

P G & E CORP              COMMON     69331C108       211      6,200 SH       SOLE                                  0           6,200

PEABODY ENERGY CORP       COMMON     704549104     2,494     53,800 SH       SOLE                             53,800               0

PENN NATIONAL 
  GAMING INC              COMMON     707569109     2,342     79,700 SH       SOLE                             79,700               0

PFIZER INC                COMMON     717081103     5,252    199,925 SH       SOLE                            195,975           3,950

PITNEY BOWES INC          COMMON     724479100     3,903     86,500 SH       SOLE                             86,500               0

PNC FINANCIAL SVCS 
  GROUP INC               COMMON     693475105     3,634     70,600 SH       SOLE                             70,600               0

PPG INDUSTRIES INC        COMMON     693506107     4,162     58,200 SH       SOLE                             58,200               0

PREMCOR INC               COMMON     74045Q104     2,530     42,400 SH       SOLE                             42,400               0

PULTE HOMES INC           COMMON     745867101     1,848     25,100 SH       SOLE                             25,100               0

QUIKSILVER INC            COMMON     74838C106    20,356    701,200 SH       SOLE                            701,200               0






Page 6 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of         CUSIP       Value       Shares or                              Other
    Name of Issuer        Class       Number    (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                          
REGIONS FINL CORP         COMMON     7591EP100     3,600    111,100 SH       SOLE                            111,100               0

RELIANT ENERGY INC        COMMON     75952B105    15,910  1,398,100 SH       SOLE                          1,398,100               0

RYDER SYSTEM INC          COMMON     783549108     1,443     34,600 SH       SOLE                             34,600               0

SARA LEE CORP             COMMON     803111103     3,573    161,228 SH       SOLE                            160,000           1,228

SBC COMMUNICATIONS INC    COMMON     78387G103    11,707    494,171 SH       SOLE                            482,800          11,371

SEARS HOLDING CORP        COMMON     812350106    28,192    211,700 SH       SOLE                            211,700               0

SIERRA HEALTH SERVICES    COMMON     826322109    22,108    346,300 SH       SOLE                            346,300               0

SIERRA PACIFIC 
  RESOURCES               COMMON     826428104     1,923    178,900 SH       SOLE                            178,900               0

STEEL DYNAMICS INC        COMMON     858119100     1,530     44,400 SH       SOLE                             44,400               0

SUNOCO INC                COMMON     86764P109     2,340     22,600 SH       SOLE                             22,600               0

TELEFONICA DE 
  ARGENTINA CONT           ADR       879991016         0     12,900 SH       SOLE                             12,900               0

TELEFONICA DE 
  ARGENTINA CONT           ADR       879991024         0     12,900 SH       SOLE                             12,900               0

TELEFONOS DE MEX           ADR       879403780     3,892    112,700 SH       SOLE                            112,700               0

TEREX CORP                COMMON     880779103     1,775     41,000 SH       SOLE                             41,000               0

TERRA INDUSTRIES INC      COMMON     880915103    16,677  2,149,100 SH       SOLE                          2,149,100               0

TESORO PETROLEUM CORP     COMMON     881609101    24,207    653,900 SH       SOLE                            653,900               0

TEXAS INDUSTRIES INC      COMMON     882491103    16,442    305,900 SH       SOLE                            305,900               0

TOLL BROTHERS INC         COMMON     889478103    21,936    278,200 SH       SOLE                            278,200               0

TORO CO                   COMMON     891092108    20,762    234,600 SH       SOLE                            234,600               0

TOTAL SA  -ADR             ADR       89151E109     4,255     36,300 SH       SOLE                             36,300               0

U G I CORPORATION NEW     COMMON     902681105       382      8,400 SH       SOLE                                  0           8,400






Page 7 of 7


                                                     FORM 13F INFORMATION TABLE

                                         Name of Reporting Manager: Hennessy Advisors, Inc.

                                                                                                    Column
      Column 1:         Column 2:    Column 3:   Column 4:    Column 5:              Column 6:         7:           Column 8:
-----------------------------------------------------------------------------------------------------------------------------------
                          Title                   Market                                           
                           of        CUSIP        Value       Shares or                              Other
    Name of Issuer        Class      Number     (x$1,000)  Principal Amount  Investment Discretion   Mgrs.      Voting Authority
-----------------------------------------------------------------------------------------------------------------------------------
                                                                   SH/ Put/        Shared   Shared     
                                                                   PRN Call  Sole  Defined   Other           Sole    Shared    None
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                             
U S BANCORP               COMMON    902973304      3,792    131,575 SH       SOLE                            131,500              75
                                               
USG CORP                  COMMON    903293405     15,715    473,900 SH       SOLE                            473,900               0
                                               
VALERO ENERGY CORP        COMMON    91913Y100     33,880    462,400 SH       SOLE                            462,400               0
                                               
VERIZON COMMUNICATIONS    COMMON    92343V104      6,350    178,863 SH       SOLE                            163,150          15,713
                                               
WACHOVIA CORP             COMMON    929903102      3,645     71,600 SH       SOLE                             71,600               0
                                               
WASHINGTON MUTUAL INC     COMMON    939322103      3,751     94,950 SH       SOLE                             94,500             450
                                               
WELLS FARGO & CO          COMMON    949746101      4,771     79,775 SH       SOLE                             62,000          17,775
                                               
WESCO INTL INC            COMMON    95082P105     18,029    643,900 SH       SOLE                            643,900               0
                                               
WESTAMERICA BANCORP       COMMON    957090103        542     10,473 SH       SOLE                                  0          10,473
                                               
XL CAPITAL LTD             ADR        sedol        3,561     49,200 SH       SOLE                             49,200               0
                                     2283401   
                                               
YELLOW ROADWAY CORP       COMMON    985577105     20,056    342,600 SH       SOLE                            342,600               0
                                               
              TOTAL                            1,340,526