To collect data on serious adverse events which occur during extended treatment with Avonex in subjects at high risk for developing multiple sclerosis (MS) and in subjects with secondary progressive MS.

Inclusion Criteria:

• Must have completed (as defined below) one of the following Biogen AVONEX® clinical studies and meet the other criteria indicated.
• Subjects enrolled from studies C95-812 and C97-830 must have completed their respective study within 12 months prior to enrollment in C98-838. Subjects enrolled from study C96-823 must have completed the study within 24 months prior to enrollment in C98-838.
• have not been diagnosed with any other disease that accounts for their neurologic symptoms.

Exclusion Criteria:

• History of any significant cardiac, hepatic, pulmonary, or renal disease; immune deficiency; or other medical conditions that would preclude therapy with interferon beta.
• History of severe allergic or anaphylactic reactions or history of hypersensitivity to human albumin.
• History of seizure within the 3 months prior to enrollment.
• Abnormal laboratory results at the screening visit:
• History of suicidal ideation or an episode of severe depression within the 3 months prior to enrollment into this study.

Other inclusion and exclusion criteria apply as per Biogen Idec Protocol