FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person *   Hamm Robert A 2. Date of Event Requiring Statement (Month/Day/Year) 10/11/2005 3. Issuer Name and Ticker or Trading Symbol BIOGEN IDEC INC [BIIB] (Last) (First) (Middle) BIOGEN IDEC INC., 14 CAMBRIDGE CENTER 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SVP, Immunology Business Unit 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) CAMBRIDGE, MA 02142 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Common Stock 9,494.434 (1) D Â

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (right-to-buy) (2)	12/09/2000(3)	12/09/2009	Common Stock	28,750	$ 62.28	D	Â
Stock Option (right-to-buy) (2)	12/15/2001(4)	12/15/2010	Common Stock	5,750	$ 45.46	D	Â
Stock Option (right-to-buy) (2)	12/14/2002(5)	12/14/2011	Common Stock	10,062	$ 49.03	D	Â
Stock Option (right-to-buy) (2)	12/06/2003(6)	12/06/2012	Common Stock	20,124	$ 37.45	D	Â
Stock Option (right-to-buy) (2)	12/31/2004(7)	02/06/2014	Common Stock	27,475	$ 43.45	D	Â
Stock Option (right-to-buy) (2)	02/17/2006(8)	02/17/2015	Common Stock	45,000	$ 67.57	D	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Hamm Robert A BIOGEN IDEC INC. 14 CAMBRIDGE CENTER CAMBRIDGE, MA 02142	Â	Â	  SVP, Immunology Business Unit	Â

Signatures

By: Benjamin S. Harshbarger; For: Robert Hamm		10/21/2005
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Number of directly held shares consists of 336.4340 shares acquired through the Issuer's Employee Stock Purchase Plan and a grant 9158 shares of Restricted Stock which fully vest on 02/06/2007.
(2)	Granted under one of the Issuer's stock option plans, in an exempt transaction under SEC rule 16(b)-3(d).
(3)	The stock option became exercisable in five (5) equal annual installments, commencing one year after the grant date of 12/09/99.
(4)	The stock option becomes exercisable in five (5) equal annual installments, commencing one year after the grant date of 12/15/00.
(5)	The stock option became exercisable in four (4) equal annual installments, commencing one year after the grant date of 12/14/01.
(6)	The stock option became exercisable in four (4) equal annual installments, commencing one year after the grant date of 12/06/02.
(7)	The stock option becomes exercisable in four (4) equal annual installments on 12/31/04, 12/31/05, 12/31/06 and 12/31/07.
(8)	The stock option becomes exercisable in four (4) equal annual installments, commencing one year after the grant date of 02/17/05.

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