OBJECTIVE: To assess long-term (up to 2 years) efficacy, tolerability, and safety of erenumab for the prevention of episodic migraine (EM) in Japanese patients. BACKGROUND: Previously published results from the double-blind treatment phase (DBTP) of a phase 2 clinical study have demonstrated the efficacy and safety of erenumab in Japanese patients with EM. METHODS: Patients completing the 24-week placebo-controlled DBTP could continue into the 76-week open-label treatment phase (OLTP), receiving erenumab 70 mg or 140 mg subcutaneously once monthly. The initial dose in the OLTP was erenumab 70 mg monthly, which was later changed to 140 mg. After study completion, the following were assessed: change from baseline in monthly migraine days (MMD), change from baseline in monthly acute migraine-specific medication days (MSMD), percentage of patients achieving ≥50% and ≥75% reduction in MMD, change from baseline in the 6-item Headache Impact Test (HIT-6™) score, and safety (exposure-adjusted patient-incidence of adverse events [AEs], calculated as number of patients per 100 patient-years). RESULTS: Of 475 patients enrolled in the DBTP, 459 (96.6%) continued in the OLTP. The mean (SD) MMD was 7.9 (2.3) at baseline with the overall change from baseline at week 100 of -2.9 (4.1) days. The monthly acute MSMD was 5.7 (2.8) at baseline with change from baseline at week 100 of -1.7 (3.7) days. The proportion of patients who achieved ≥50% and ≥75% reduction in MMD from baseline at week 100 was 177/398 (44.5%) and 94/398 (23.6%), respectively. The HIT-6™ score was 58.4 (5.4) at baseline with a change of -6.4 (8.2) at week 100. The exposure-adjusted patient-incidence of AEs during the OLTP was 207.1/100 patient-years for the combined erenumab group, similar to that observed for either erenumab (271.0/100 patient-years) or placebo (257.3/100 patient-years) during the DBTP, and no new safety signals were detected during the OLTP. CONCLUSION: Long-term erenumab treatment in Japanese patients with EM demonstrated sustained efficacy for up to 2 years, with a safety profile similar to previous studies, supporting erenumab as a potential new therapy for EM prevention in Japan.