BIOGEN INC. — Director's Dealing 2011

Feb 25, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: BIOGEN IDEC INC. (BIIB)
CIK: 0000875045
Period of Report: 2011-02-23

Reporting Person: Cox John (EVP Pharmaceutical Oper & Tech)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2011-02-23	Common Stock	M	1733	—	Acquired	15336.0411	Direct
2011-02-23	Common Stock	M	405	—	Acquired	15741.0411	Direct
2011-02-23	Common Stock	F	551	$66.76	Disposed	15190.0411	Direct
2011-02-23	Common Stock	F	129	$66.76	Disposed	15061.0411	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-02-23	Restricted Stock Unit	$0	M	1733	Disposed	2014-02-23	Common Stock (1733)	Direct
2011-02-23	Restricted Stock Unit	$0	M	405	Disposed	2014-02-23	Common Stock (405)	Direct
2011-02-23	Restricted Stock Unit	$0	J	462	Disposed	2014-02-23	Common Stock (0)	Direct

Footnotes

F1: There is no conversion or exercise price for this stock unit.

F2: The number of RSUs reported represents the maximum possible number of shares that are eligible for vesting, which is 150% of the number of shares at target payout. One-fourth of these RSUs are eligible to vest on each of the first four anniversaries of the grant date. The actual number of shares that will vest on each vesting date will be determined by comparing the price of Biogen Idec common stock on such vesting date to the price on the grant date (i.e., number of vested shares = number of shares at target payout times [the average 60 calendar-day closing stock price ending on the vesting date divided by the average 60 calendar-day closing stock price on the grant date]).

F3: This represents the difference between the maximum possible number of shares that were eligible for vesting and the actual number that vested.