SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G (Rule 13d-102) INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1 (b), (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b) (Amendment No. 3)* Alnylam Pharmaceuticals, Inc. ------------------------------------------------------------------------------ (Name of Issuer) Common Stock ------------------------------------------------------------------------------ (Title of Class of Securities) 02043Q107 ------------------------------------------------------------------------------ (CUSIP Number) December 30, 2005 ------------------------------------------------------------------------------ (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: Rule 13d-1(b) Rule 13d-1(c) X Rule 13d-1(d) *The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page. The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes). (Continued on following pages) Page 1 of 16 Exhibit Index on Page 13 CUSIP NO. 02043Q107 13 G Page 2 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Polaris Venture Partners III, L.P. ("PVP III") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware 5 SOLE VOTING POWER NUMBER OF 365,852 shares, except that Polaris Venture SHARES Management Co. III, L.L.C. ("Polaris III"), the BENEFICIALLY general partner of PVP III, may be deemed to OWNED BY EACH REPORTING have sole power to vote these shares, and PERSON Jonathan A. Flint ("Flint"), Terrance G. McGuire WITH ("McGuire") and Alan G. Spoon ("Spoon"), the managing members of Polaris III, may be deemed to have shared power to vote these shares. 6 SHARED VOTING POWER See response to row 5. 7 SOLE DISPOSITIVE POWER 365,852 shares, except that Polaris III, the general partner of PVP III, may be deemed to have sole power to dispose of these shares, and Flint, McGuire and Spoon, the managing members of Polaris III, may be deemed to have shared power to dispose of these shares. 8 SHARED DISPOSITIVE POWER See response to row 7. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 365,852 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 1.37% 12 TYPE OF REPORTING PERSON PN CUSIP NO. 02043Q107 13 G Page 3 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Polaris Venture Partners Entrepreneurs' Fund III, L.P. ("Entrepreneurs' III") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware 5 SOLE VOTING POWER NUMBER OF 9,372 shares, except that Polaris III, the SHARES general partner of Entrepreneurs' III, may be BENEFICIALLY deemed to have sole power to vote these shares, OWNED BY EACH REPORTING and Flint, McGuire and Spoon, the managing PERSON members of Polaris III, may be deemed to have WITH shared power to vote these shares. 6 SHARED VOTING POWER See response to row 5. 7 SOLE DISPOSITIVE POWER 9,372 shares, except that Polaris III, the general partner of Entrepreneurs' III, may be deemed to have sole power to dispose of these shares, and Flint, McGuire and Spoon, the managing members of Polaris III, may be deemed to have shared power to dispose of these shares. 8 SHARED DISPOSITIVE POWER See response to row 7. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 9,372 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.04% 12 TYPE OF REPORTING PERSON PN CUSIP NO. 02043Q107 13 G Page 4 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Polaris Venture Partners Founders' Fund III, L.P. ("Founders' III") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware 5 SOLE VOTING POWER NUMBER OF 5,701 shares, except that Polaris III, the SHARES general partner of Founders' III, may be deemed BENEFICIALLY to have sole power to vote these shares, and OWNED BY EACH REPORTING Flint, McGuire and Spoon, the managing members PERSON of Polaris III, may be deemed to have shared WITH power to vote these shares. 6 SHARED VOTING POWER See response to row 5. 7 SOLE DISPOSITIVE POWER 5,701 shares, except that Polaris III, the general partner of Founders' III, may be deemed to have sole power to dispose of these shares, and Flint, McGuire and Spoon, the managing members of Polaris III, may be deemed to have shared power to dispose of these shares. 8 SHARED DISPOSITIVE POWER See response to row 7. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,701 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.02% 12 TYPE OF REPORTING PERSON PN CUSIP NO. 02043Q107 13 G Page 5 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Polaris Venture Management Co. III, L.L.C. ("Polaris III") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware 5 SOLE VOTING POWER NUMBER OF 380,925 shares, of which 365,852 are directly SHARES owned by PVP III, 9,372 are directly owned by BENEFICIALLY Entrepreneurs' III and 5,701 are directly owned OWNED BY EACH REPORTING by Founders' III. Polaris III, the general PERSON partner of PVP III, Entrepreneurs' III and WITH Founders' III, may be deemed to have sole power to vote these shares, and Flint, McGuire and Spoon, the managing members of Polaris III, may be deemed to have shared power to vote these shares. 6 SHARED VOTING POWER See response to row 5. 7 SOLE DISPOSITIVE POWER 380,925 shares, of which 365,852 are directly owned by PVP III, 9,372 are directly owned by Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III, the general partner of PVP III, Entrepreneurs' III and Founders' III, may be deemed to have sole power to vote these shares, and Flint, McGuire and Spoon, the managing members of Polaris III, may be deemed to have shared power to dispose of these shares. 8 SHARED DISPOSITIVE POWER See response to row 7. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 380,925 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 1.43% 12 TYPE OF REPORTING PERSON OO CUSIP NO. 02043Q107 13 G Page 6 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Jonathan A. Flint ("Flint") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION U.S. Citizen 5 SOLE VOTING POWER 0 shares. NUMBER OF SHARES BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH REPORTING 380,925 shares, of which 365,852 are directly PERSON owned by PVP III, 9,372 are directly owned by WITH Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. Flint is a managing member of Polaris III, and may be deemed to have shared power to vote these shares. 7 SOLE DISPOSITIVE POWER 0 shares. 8 SHARED DISPOSITIVE POWER 380,925 shares, of which 365,852 are directly owned by PVP III, 9,372 are directly owned by Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. Flint is a managing member of Polaris III, and may be deemed to have shared power to dispose of these shares. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 380,925 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 1.43% 12 TYPE OF REPORTING PERSON IN CUSIP NO. 02043Q107 13 G Page 7 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Terrance G. McGuire ("McGuire") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION U.S. Citizen 5 SOLE VOTING POWER 0 shares. NUMBER OF SHARES BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH REPORTING 380,925 shares, of which 365,852 are directly PERSON owned by PVP III, 9,372 are directly owned by WITH Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. McGuire is a managing member of Polaris III, and may be deemed to have shared power to vote these shares. 7 SOLE DISPOSITIVE POWER 0 shares. 8 SHARED DISPOSITIVE POWER 380,925 shares, of which 365,852 are directly owned by PVP III, 9,372 are directly owned by Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. McGuire is a managing member of Polaris III, and may be deemed to have shared power to dispose of these shares. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 380,925 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 1.43% 12 TYPE OF REPORTING PERSON IN CUSIP NO. 02043Q107 13 G Page 8 of 16 1 NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Alan G. Spoon ("Spoon") 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) (b) X 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION U.S. Citizen 5 SOLE VOTING POWER 0 shares. NUMBER OF SHARES BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH REPORTING 380,925 shares, of which 365,852 are directly PERSON owned by PVP III, 9,372 are directly owned by WITH Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. Spoon is a managing member of Polaris III, and may be deemed to have shared power to vote these shares. 7 SOLE DISPOSITIVE POWER 0 shares. 8 SHARED DISPOSITIVE POWER 380,925 shares, of which 365,852 are directly owned by PVP III, 9,372 are directly owned by Entrepreneurs' III and 5,701 are directly owned by Founders' III. Polaris III is the general partner of PVP III, Entrepreneurs' III and Founders' III. Spoon is a managing member of Polaris III, and may be deemed to have shared power to dispose of these shares. 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 380,925 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 1.43% 12 TYPE OF REPORTING PERSON IN CUSIP NO. 02043Q107 13 G Page 9 of 16 ITEM 1(A). NAME OF ISSUER Alnylam Pharmaceuticals, Inc. ITEM 1(B). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES 300 Third Street Cambridge, Massachusetts 02142 ITEM 2(A). NAME OF PERSONS FILING This Statement is filed by Polaris Venture Partners III, L.P., a Delaware limited partnership ("PVP III"), Polaris Venture Partners Entrepreneurs' Fund III, L.P., a Delaware limited partnership ("Entrepreneurs' III"), Polaris Venture Partners Founders' Fund III, L.P., a Delaware limited partnership ("Founders' III"), Polaris Venture Management Co. III, L.L.C., a Delaware limited liability company ("Polaris III"), Jonathan A. Flint ("Flint"), Terrance G. McGuire ("McGuire") and Alan G. Spoon ("Spoon"). Flint, McGuire and Spoon are the managing members of Polaris III. The foregoing entities and individuals are collectively referred to as the "Reporting Persons." Polaris III, the general partner of PVP III, Entrepreneurs' III and Founders' III, may be deemed to have sole power to vote and sole power to dispose of shares of the issuer directly owned by PVP III, Entrepreneurs' III and Founders' III. Flint, McGuire and Spoon are the managing members of Polaris III and may be deemed to have shared power to vote and shared power to dispose of shares of the issuer directly owned by PVP III, Entrepreneurs' III and Founders' III. ITEM 2(B). ADDRESS OF PRINCIPAL OFFICE The address for each of the Reporting Persons is: Polaris Venture Partners 1000 Winter Street, Suite 3350 Waltham, Massachusetts 02451 ITEM 2(C) CITIZENSHIP PVP III, Entrepreneurs' III and Founders' III are Delaware limited partnerships; Polaris III is a Delaware Limited Liability Company; Flint, McGuire and Spoon are United States citizens. ITEM 2(D) AND (E). TITLE OF CLASS OF SECURITIES AND CUSIP NUMBER Common Stock CUSIP # 02043Q107 ITEM 3. Not Applicable ITEM 4. OWNERSHIP The following information with respect to the ownership of the Common Stock of the issuer by the persons filing this Statement is provided as of December 30, 2005: (a) Amount beneficially owned: See Row 9 of cover page for each Reporting Person. (b) Percent of Class: CUSIP NO. 02043Q107 13 G Page 10 of 16 See Row 11 of cover page for each Reporting Person. (c) Number of shares as to which such person has: (i) Sole power to vote or to direct the vote: See Row 5 of cover page for each Reporting Person. (ii) Shared power to vote or to direct the vote: See Row 6 of cover page for each Reporting Person. (iii) Sole power to dispose or to direct the disposition of: See Row 7 of cover page for each Reporting Person. (iv) Shared power to dispose or to direct the disposition of: See Row 8 of cover page for each Reporting Person. ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS. Not applicable. ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON. Under certain circumstances set forth in the limited partnership agreements of PVP III, Entrepreneurs' III and Founders' III, the general and limited partners of each of such entities may be deemed to have the right to receive dividends from, or the proceeds from, the sale of shares of the issuer owned by each such entity of which they are a partner. ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY Not applicable. ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP. Not applicable. ITEM 9. NOTICE OF DISSOLUTION OF GROUP. Not applicable. ITEM 10. CERTIFICATION. Not applicable. Page 11 of 16 SIGNATURES After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. Dated: February 22, 2006 POLARIS VENTURE PARTNERS III, L.P., /s/ Kevin Littlejohn a Delaware Limited Partnership ----------------------------------- Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE PARTNERS /s/ Kevin Littlejohn ENTREPRENEURS' FUND III, L.P., ------------------------------------ a Delaware Limited Partnership Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE PARTNERS /s/ Kevin Littlejohn FOUNDERS' FUND III, L.P., ------------------------------------ a Delaware Limited Partnership Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE MANAGEMENT CO. III, L.L.C., /s/ Kevin Littlejohn a Delaware Limited Liability Company ------------------------------------ Signature Kevin Littlejohn Authorized Signatory JONATHAN A. FLINT /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory Page 12 of 16 TERRANCE G. MCGUIRE /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory ALAN G. SPOON /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory Page 13 of 16 EXHIBIT INDEX Found on Sequentially Exhibit Numbered Page ------- ------------- Exhibit A: Agreement of Joint Filing 14 Exhibit B: Reference to Kevin Littlejohn as Authorized Signatory 16 Page 14 of 16 EXHIBIT A Agreement of Joint Filing The undersigned hereby agree that a single Schedule 13G (or any amendment thereto) relating to the Common Stock of Alnylam Pharmaceuticals, Inc. shall be filed on behalf of each of the undersigned and that this Agreement shall be filed as an exhibit to such Schedule 13G. Dated: February 22, 2006 POLARIS VENTURE PARTNERS III, L.P., /s/ Kevin Littlejohn a Delaware Limited Partnership ------------------------------------ Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE PARTNERS /s/ Kevin Littlejohn ENTREPRENEURS' FUND III, L.P., ------------------------------------ a Delaware Limited Partnership Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE PARTNERS /s/ Kevin Littlejohn FOUNDERS' FUND III, L.P., ------------------------------------ a Delaware Limited Partnership Signature Kevin Littlejohn Authorized Signatory POLARIS VENTURE MANAGEMENT CO. III, L.L.C., /s/ Kevin Littlejohn a Delaware Limited Liability Company ------------------------------------ Signature Kevin Littlejohn Authorized Signatory JONATHAN A. FLINT /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory Page 15 of 16 TERRANCE G. MCGUIRE /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory ALAN G. SPOON /s/ Kevin Littlejohn ------------------------------------ Signature Kevin Littlejohn Authorized Signatory Page 16 of 16 EXHIBIT B REFERENCE TO KEVIN LITTLEJOHN AS AUTHORIZED SIGNATORY Kevin Littlejohn has signed the enclosed documents as Authorized Signatory. Note that copies of the applicable Agreement to File Jointly and Statement Appointing Designated Filer and Authorized Signatory are already on file with the appropriate agencies.