UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

x

Rule 13d-1(b)

o

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 45784P101

1.

Names of Reporting Persons
Fred Alger Management, Inc.         13-2510833

Alger Associates, Incorporated       13-3017981

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

x

3.

SEC Use Only

4.

Citizenship or Place of Organization
New York, New York

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
3,435,241

6.

Shared Voting Power
-0-

7.

Sole Dispositive Power
3,435,241

8.

Shared Dispositive Power
-0-

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,435,241

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
9.34%

12.

Type of Reporting Person (See Instructions)
Fred Alger Management, Inc.         IA

Alger Associates, Incorporated       HC

CUSIP No. 45784P101

Item 1.

(a)

Name of Issuer
INSULET CORPORATION

(b)

Address of Issuer’s Principal Executive Offices
9 Oak Park Drive
Bedford, MA 01730

Item 2.

(a)

Name of Person Filing
1.                                       Fred Alger Management, Inc.*

2.                                       Alger Associates, Incorporated

(b)

Address of Principal Business Office or, if none, Residence
111 Fifth Avenue, New York, NY 10003

(c)

Citizenship
New York

(d)

Title of Class of Securities
Common Stock

(e)

CUSIP Number
45784P101

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8).

(e)

x

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

(h)

o

A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

A non-U.S. institution in accordance with § 240.13d–1(b)(1)(ii)(J);

(k)

o

Group, in accordance with § 240.13d–1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with § 240.13d–1(b)(1)(ii)(J), please specify the type of institution:____________________________

CUSIP No. 45784P101

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   

3,435,241

(b)

Percent of class:    

9.34%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

3,435,241

(ii)

Shared power to vote or to direct the vote    

-0-

(iii)

Sole power to dispose or to direct the disposition of   

3,435,241

(iv)

Shared power to dispose or to direct the disposition of   

-0-

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   o.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

n/a

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

n/a

Item 8.

Identification and Classification of Members of the Group

n/a

Item 9.

Notice of Dissolution of Group

n/a

Item 10.

Certification

(a)  The following certification shall be included if the statement is filed pursuant to s240.13d-1(b):

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

FRED ALGER MANAGEMENT, INC.

By:

/s/ Hal Liebes

Executive Vice President

January 28, 2010

ALGER ASSOCIATES, INC.

By:

/s/ Hal Liebes

Director

January 28, 2010