The purpose of this study is to evaluate the long-term safety, tolerability and activity of Fampridine-SR in subjects with multiple sclerosis who have previously participated in either an Acorda Therapeutics or an Elan Corporation sponsored protocol. Subjects are eligible regardless of whether they received active drug or placebo during their participation in the previous study.

Under the original protocol, patients were to have their treatment dose titrated upwards from a starting dose of 10mg b.i.d. to 15mg b.i.d. and then to a stable (maintenance) dose of 20mg b.i.d. The protocol was subsequently revised to lower the maximum maintenance dose. In the most current protocol, all patients were down-titrated to 10mg b.i.d. and maintained at this dose for the greater part of the duration of the study.

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:

• The subject must have been previously enrolled in an Acorda Therapeutics or an Elan Corporation sponsored study for multiple sclerosis and received either Fampridine or placebo.
• The subject must have multiple sclerosis as determined by the Principal Investigator.
• The subject, male or female, 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.
• The subject must be of adequate cognitive function, as judged by the Investigator.
• Any subject who is female and of childbearing potential, regardless of sexual activity, must have a negative urine pregnancy test at the Screening Visit.

Exclusion Criteria:

• The subject is a female who is either pregnant or breastfeeding, or of child-bearing potential, who, if engaged in active heterosexual relations and has not had a hysterectomy or bilateral oophorectomy, would not use one of the following birth control methods: tubal ligation, implantable contraception device, oral, injectable or transdermal contraceptive, barrier method or sexual activity restricted to vasectomized partner.
• The subject withdrew from a previous Fampridine study because of a Serious Adverse Event that was possibly, probably or definitely related to Fampridine.
• The subject has a history of seizures or has evidence of past, or possible, epileptiform activity on an EEG.
• The subject has either a clinically significant abnormal ECG or laboratory value(s) at the Screening Visit, as judged by the Investigator
• The subject has angina, uncontrolled hypertension, clinically significant cardiac arrhythmias, or any other clinically significant cardiovascular abnormality, as judged by the Investigator.
• The subject has a known allergy to pyridine-containing substances or any of the inactive ingredients of the Fampridine tablet
• The subject has received an investigational drug, except for Fampridine- SR (or matching placebo) under Protocol MS-F202, within 30 days prior to the Screening Visit; or the subject is scheduled to enroll in an investigational drug trial at any time during this study.
• The subject has received compounded 4-aminopyridine (4-AP) within 14 days of the Screening Visit.
• The subject has had an onset of an MS exacerbation within 30 days prior to the Screening Visit, or, if in the judgment of the Investigator, has not stabilized from a prior exacerbation episode.
• The subject has started on a concomitant medication regimen for an underlying disease/symptom within the past 7 days; or has started an interferon or chemotherapeutic agent for multiple sclerosis within the past 4 weeks.
• The subject has a history of drug or alcohol abuse within the past year.