FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN 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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1. Name and Address of Reporting Person * Posner Brian S   2. Issuer Name and Ticker or Trading Symbol BIOGEN IDEC INC. [BIIB] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) BIOGEN IDEC INC., 133 BOSTON POST ROAD 3. Date of Earliest Transaction (Month/Day/Year) 05/25/2011 (Street) WESTON, MA 02493 4. If Amendment, Date Original Filed(Month/Day/Year) 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 Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/25/2011   M(1)   5,975 A $ 53.43 15,705 D   Common Stock 05/25/2011   M(1)   20,000 A $ 71.38 35,705 D   Common Stock 05/25/2011   S(1)   12,805 D $ 93.7407 (2) (4) 22,900 D   Common Stock 05/25/2011   S(1)   13,170 D $ 94.4326 (3) (4) 9,730 D

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Stock Option (Right to Buy) (5)

$ 53.43

05/25/2011

M(1)

5,975

06/03/2010

06/02/2019

Common Stock

5,975

$ 0

0

D

Stock Option (Right to Buy)

$ 71.38

05/25/2011

M(1)

20,000

(6)

07/22/2018

Common Stock

20,000

$ 0

15,000

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Posner Brian S BIOGEN IDEC INC. 133 BOSTON POST ROAD WESTON, MA 02493	X

Signatures

Aras Lapinskas, Attorney in Fact for Brian S. Posner		05/27/2011
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(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)	Exercise/sale pursuant to a trading plan intended to comply with Rule 10b5-1 of the Securities Exchange Act of 1934.
(2)	This represents the weighted average price for shares sold at a range between $93.18 (low) and $94.16 (high).
(3)	This represents the weighted average price for shares sold at a range between $94.19 (low) and $94.67 (high).
(4)	Full information regarding the number of shares sold at each separate price will be provided upon request by the SEC staff, the issuer, or a security holder of the issuer.
(5)	Granted under one of the Issuer's stock option plans, in an exempt transaction under SEC Rule 16(b)-3(d).
(6)	The stock options become exercisable in three (3) equal annual installments, commencing one year after the grant date of 07/23/2008.

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