Abstract Objective To evaluate the long-term efficacy and safety of brodalumab, a fully human anti–interleukin-17 receptor A monoclonal antibody, in patients with axial spondyloarthritis (axSpA). Methods Patients receiving subcutaneous brodalumab 210 mg during the 16-week double-blind period of this multicentre, phase 3 study conducted across Japan, Korea and Taiwan continued the same during the 52-week open-label extension, whereas patients receiving placebo switched to brodalumab 210 mg at week 16. Efficacy [Assessment of SpondyloArthritis International Society (ASAS) 40 and ASAS 20 response rates; change from baseline in AS Disease Activity Score using CRP (ASDAS-CRP)] and safety were evaluated. Results Overall, 145 patients (brodalumab, n = 77; placebo, n = 68) received brodalumab during the open-label extension. ASAS 40 response rates (95% CI) of 56.3% (44.7%, 67.3%) and 57.4% (44.1%, 70.0%) were achieved in the brodalumab and placebo groups, respectively, at week 68. ASAS 20 response rates (95% CI) achieved at week 68 in both treatment groups were similar [brodalumab, 71.3% (60.0%, 80.8%); placebo, 78.7% (66.3%, 88.1%)]. The least squares mean change (95% CI) in ASDAS-CRP at week 68 suggested a clinically important improvement (change, ≥1.1) in both treatment groups [brodalumab, –1.528 (–1.737, –1.319); placebo, –1.586 (–1.815, –1.357)]. The exposure-adjusted event rates (per 100 patient-years) for treatment-emergent adverse events (TEAEs) and drug-related TEAEs were 255.9 and 147.9, respectively; nasopharyngitis (35.6) and upper respiratory tract infection (14.7) were the most common TEAEs. Conclusions Brodalumab demonstrated sustained efficacy and a consistent safety profile in patients with axSpA over 68 weeks. Study registration ClinicalTrials.gov, https://clinicaltrials.gov, NCT02985983