The long-term safety and efficacy of filgotinib (from phase 2 studies), with or without methotrexate (MTX), for the treatment of patients with rheumatoid arthritis was assessed in DARWIN 3, a long-term, open-label extension study (NCT02065700).Eligible patients completing the 24-week DARWIN 1 (filgotinib + MTX) and DARWIN 2 (filgotinib monotherapy) studies entered DARWIN 3, where they received filgotinib 200 mg/day, except for 15 men who received filgotinib 100 mg/day. Safety analyses were performed using the safety analysis set and exposure-adjusted incidence rate (EAIR) of treatment-emergent adverse events (TEAEs) was calculated. Efficacy was assessed from baseline in the parent studies.Of 790 patients completing the phase 2 parent studies, 739 enrolled in the study. Through April 2019, 59.5% of patients had received ≥4 years of study drug. Mean (SD) exposure to filgotinib was 3.55 (1.57) years in the filgotinib + MTX group and 3.38 (1.59) years in the filgotinib monotherapy group. EAIR per 100 patient years of exposure (PYE) for TEAEs was 24.6 in the filgotinib + MTX group and 25.8 in the filgotinib monotherapy group, and for serious TEAEs, the EAIR was 3.1 and 4.3, respectively. ACR20/50/70 responses among patients remaining in the study could be maintained through 4 years, with 89.3%/69.6%/49.1% of filgotinib + MTX group and 91.8%/69.4%/44.4% of monotherapy group maintaining ACR20/50/70 responses based on observed data.Filgotinib was well tolerated with a 4-year safety profile comparable to that of the parent trials, both in patients receiving combination therapy with MTX or as monotherapy.