The purpose of this study is to evaluate the safety, tolerability and activity of Fampridine-SR when administered for up to 36 additional months, or until it becomes commercially available whichever comes first, in subjects who previously participated in Acorda Therapeutics Protocol MS-F203.

Multiple Sclerosis (MS) is a disorder of the body's immune system that affects the central nervous system (CNS). Normally, nerve fibers carry electrical impulses through the spinal cord, providing communication between the brain and the arms and legs. In people with MS, the fatty sheath that surrounds and insulates the nerve fibers (called "myelin") deteriorates, causing nerve impulses to be slowed or stopped. As a result, patients with MS may experience periods of muscle weakness and other symptoms such as numbness, loss of vision, loss of coordination, paralysis, spasticity, mental and physical fatigue and a decrease in the ability to think and/or remember. These periods of illness may come (exacerbations) and go (remissions). Fampridine-SR is an experimental drug that has been reported to possibly improve muscle strength and walking ability for some people with MS. This study will evaluate the effects and possible risks of taking Fampridine-SR in MS patients over a long period of time.

Inclusion Criteria:

• subject must have been previously enrolled in Acorda Therapeutics MS-F203 study for multiple sclerosis and received either Fampridine-SR or placebo
• subject is a man or woman with clinical definite multiple sclerosis as defined by McDonald (McDonald WI, et al. Recommended Diagnostic Criteria for Multiple Sclerosis; Guidelines from the International Panel on the Diagnosis of Multiple Sclerosis; Annals of Neurology. 2001; 50: 121-127)
• subject must be at least 18 years of age. Any subject who is now over the age of 70 must be in good overall health in the judgment of the Investigator
• subject must be of adequate cognitive function, as judged by the Investigator, to understand and sign the IRB/REB-approved informed consent form prior to the performance of any study-specific procedures and is willing to comply with the required scheduling and assessments of the protocol
• subjects who are women of childbearing potential, regardless of sexual activity, must have a negative urine pregnancy test at the Screening Visit.

Exclusion Criteria:

• women who are either pregnant or breastfeeding, and women of childbearing potential (defined as not surgically sterile or at least two years post menopausal) who are engaged in active heterosexual relations and, are not using one of the following birth control methods: tubal ligation, implantable contraception device, oral, patch, injectable or transdermal contraceptive, barrier method or sexual activity restricted to vasectomized partner.
• subject discontinued prematurely from the MS-F203 study
• subject has a history of seizures or has evidence of past, or possible, epileptiform activity on an EEG
• subject has either a clinically significant abnormal ECG or laboratory value(s) at the Screening visit, as judged by the Investigator that would preclude entry into the study. ECG and laboratory results from Visit 6 or repeat results from Visit 7 of the MS-F203 study may be used as the baseline for the current study
• subject has angina, uncontrolled hypertension, clinically significant cardiac arrhythmias, or any other clinically significant cardiovascular abnormality, as judged by the Investigator
• subject has a known allergy to pyridine-containing substances or any of the inactive ingredients of the Fampridine-SR tablet (hydroxypropyl methylcellulose, microcrystalline cellulose, colloidal silicon dioxide, magnesium stearate, opadry white (tablet film coating))
• subject has received an investigational drug, except for Fampridine-SR or matching placebo under protocol MS-F203, within 30 days of the Screening Visit. Subject is scheduled to enroll in an investigational drug trial at any time during this study.
• subject has a history of drug or alcohol abuse within the past year