Background Brodalumab (anti–interleukin-17-receptor antibody) was effective in treating moderate to severe psoriasis in a 12-week, dose-ranging, placebo-controlled trial. Objective We sought to evaluate efficacy and safety of long-term brodalumab treatment. Methods In this interim analysis at week 120 of an open-label extension study, patients received brodalumab 210 mg every 2 weeks. Protocol amendments reduced the dose (140 mg) in patients weighing 100 kg or less and subsequently increased the dose (210 mg) in patients with inadequate responses. Efficacy was measured by static physician global assessment and 75% or greater, 90% or greater, or 100% improvement in Psoriasis Area and Severity Index score (PASI-75, PASI-90, and PASI-100, respectively). Results Of 181 patients, 144 completed week 120. Static physician global assessment scores of clear/almost clear and clear were achieved by 90% and 63% of patients, respectively, at week 12 and by 72% and 51% at week 120. The PASI-75, PASI-90, and PASI-100 response rates at week 12 (95%/85%/63%) were sustained through week 120 (86%/70%/51%). Most commonly reported adverse events were nasopharyngitis (26.5%), upper respiratory tract infection (19.9%), arthralgia (16.0%), and back pain (11.0%). Four patients had grade-2 absolute neutrophil count. Limitations There was no control group in this open-label extension. Conclusion Brodalumab demonstrated sustained clinical response and an acceptable safety profile through 120 weeks in patients with moderate to severe psoriasis.