NEW YORK, Dec 10 - William Young is set to become chairman of Biogen Idec Inc's(BIIB.O) board of directors when Bruce Ross steps down from the post on Jan. 1, the biotechnology company announced on Thursday.

Ross, 68, who has been Biogen's chairman since Dec. 2005 and a director for 13 years, will complete his current term as director and retire from the board at the company's 2010 annual shareholder meeting. The date of that meeting has not yet been set.

Until recently, Young was chairman and chief executive of Monogram Biosciences, which was acquired by Laboratory Corporation of America (LH.N). Prior to that, Young was chief operating officer at Genentech.

Cambridge, Massachusetts-based Biogen, which sells the multiple sclerosis drugs Avonex and Tysabri, also announced that former Thermo Fisher Scientific(TMO.N) CEO Marijn Dekkers is leaving its board at the end of the month.

Dekkers, a member of the Biogen board since 2007, is about to become chief executive of German drugmaker Bayer (BAYGn.DE). (Reporting by Bill Berkrot, editing by Leslie Gevirtz)