The purpose of this study is to determine the effects of teriflunomide on: frequency of relapses; accumulation of disability, measured by Expanded Disability Status Scale (EDSS); burden of disease, measured by magnetic resonance imaging (MRI); subject-reported fatigue; and safety and tolerability.

The 2-years double-blind placebo controlled period is followed by a long term open-label extension study LTS6050 with two doses of Teriflunomide.

• Drug: teriflunomide (HMR1726)
• Drug: placebo

• Experimental: 7 mg
• Experimental: 14 mg

Inclusion Criteria:

• Multiple sclerosis (MS) subjects,who are ambulatory (EDSS of ≤ 5.5)
• Exhibiting a relapsing clinical course, with or without progression (relapsing remitting, secondary progressive or progressive relapsing)
• Meeting McDonald's criteria for MS diagnosis
• Experienced at least 1 relapse over the 1 year preceding the trial or at least 2 relapses over the 2 years preceding the trial
• No relapse onset in the preceding 60 days prior to randomization
• During the 4 weeks prior to randomization, subjects must have been clinically stable, without adrenocorticotrophic hormone (ACTH) or systemic steroid treatment.
• Signed informed consent form

Exclusion Criteria:

• Patients with clinically relevant cardiovascular, hepatic, neurological, endocrine or other major systemic disease
• Patients with significantly impaired bone marrow function
• Pregnant or nursing women
• Alcohol or drug abuse
• Use of cladribine, mitoxantrone, or other immunosuppressant agents such as azathioprine, cyclophosphamide, cyclosporin, methotrexate or mycophenolate before enrollment
• Any known condition or circumstance that would prevent in the investigator's opinion compliance or completion of the study