X0306 4 2013-02-12 0000875045 BIOGEN IDEC INC. BIIB 0001263839 ALEXANDER SUSAN H BIOGEN IDEC INC. 133 BOSTON POST ROAD WESTON MA 02493 1 EVP, Chief Legal Officer Restricted Stock Unit 0 2013-02-12 4 A 0 8573 0 A 2017-02-12 Common Stock 8573 8573 D 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]). Aras Lapinskas, Attorney in Fact for Susan H. Alexander 2013-02-14