BACKGROUND : In the phase 3 TOPIC study, teriflunomide significantly reduced the risk of relapse determining conversion to clinically definite multiple sclerosis (CDMS) in patients with clinically isolated syndrome, versus placebo. We assessed clinical and safety outcomes associated with extended teriflunomide treatment in the TOPIC extension study. METHODS : Patients who completed the TOPIC core study (including those still on study at early termination) or converted to CDMS after at least 24 weeks in the core study were eligible to participate in the extension. The primary efficacy endpoint in the extension was time to conversion to CDMS. RESULTS : Risk of relapse determining conversion to CDMS was 47.1% lower in patients treated with teriflunomide 14 mg during the core and extension studies compared with patients treated with placebo during the core study and teriflunomide 14 mg during the extension. The incidence of adverse events was 75.8% and 81.9% for 7 and 14 mg teriflunomide, respectively. CONCLUSIONS : Reduced risk of relapse determining conversion to CDMS in patients with early MS receiving teriflunomide 14 mg in the core study remained throughout the extension supporting the benefits of early treatment. No new safety signals were observed for teriflunomide 7 or 14 mg.