X0303 4 2011-05-02 0000875045 BIOGEN IDEC INC. BIIB 0001263839 ALEXANDER SUSAN H BIOGEN IDEC INC. 133 BOSTON POST ROAD WESTON MA 02493 1 EVP, General Counsel Common Stock 2011-05-02 4 S 0 4124 96.9682 D 35834 D Common Stock 2011-05-02 4 S 0 2876 97.5351 D 32958 D Common Stock 2011-05-02 4 S 0 3177 96.8994 D 29781 D Common Stock 2011-05-02 4 S 0 2816 97.5202 D 26965 D Common Stock 2011-05-02 4 S 0 5100 97.0221 D 21865 D Common Stock 2011-05-02 4 S 0 2900 97.5207 D 18965 D Sale pursuant to a trading plan intended to comply with Rule 10b5-1 of the Securities Exchange Act of 1934. 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. This represents the weighed average price for shares sold at a range between $96.38 (low) and $97.35 (high). This represents the weighed average price for shares sold at a range between $97.44 (low) and $97.71 (high). This represents the weighed average price for shares sold at a range between $97.38 (low) and $97.72 (high). This represents the weighed average price for shares sold at a range between $96.41 (low) and $97.40 (high). This represents the weighed average price for shares sold at a range between $97.43 (low) and $97.73 (high). Aras Lapinskas, Attorney in Fact for Susan H. Alexander 2011-05-03