The primary objective of the study is to evaluate the long-term safety and tolerability of BIIB041 (fampridine-sustained release (SR)) treatment in Canadian participants with multiple sclerosis (MS) who previously participated in the registrational and extension studies conducted by Acorda. Those studies include NCT00654927 (MS-F202EXT), NCT00648908 (MS-F203EXT) and NCT00649792 (MS-F204EXT).

Key Inclusion Criteria :

1. Previously enrolled in 1 of the 3 Acorda-sponsored studies (MS-F202EXT, MS-F203EXT, and MS-F204EXT) and continuing to receive fampridine-SR.
2. Willing to comply with the required scheduling and assessments of the protocol.
3. Female subjects of childbearing potential, regardless of sexual activity, must have a negative urine pregnancy test, and must practice effective contraception during the study and be willing and able to continue contraception for 1 month after their last dose of study treatment.

Key Exclusion Criteria:

1. Discontinued prematurely from the preceding study ((MS-F202EXT, MS-F203EXT, or MS-F204EXT).
2. Any prior history of seizure, epilepsy, or other convulsive disorder.
3. Any clinically significant abnormal laboratory values.
4. New history of moderate or severe renal impairment.
5. New history of angina, uncontrolled hypertension, clinically significant cardiac arrhythmias, or any other clinically significant cardiovascular abnormality, as judged by the Investigator.
6. Any significant change in overall health that would preclude subject's participation in the study, in the opinion of the Investigator.
7. Known allergy to pyridine-containing substances or any of the inactive ingredients of the fampridine-SR tablet
8. Received an investigational drug, except fampridine-SR under the preceding study (MS-F202EXT, MS-F203EXT, or MS-F204EXT), within the last 30 days, or the subject is scheduled to enroll in an investigational drug at any time during the study.
9. A history of drug or alcohol abuse within the past year.
10. Treatment with other forms of fampridine or 4-AP (e.g., compounded formulation of 4-AP) or 3,4-diaminopyridine (3,4-DAP).

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.