BACKGROUND AND OBJECTIVES: Ravulizumab, a complement component 5 inhibitor, was approved for the treatment of adults with anti-aquaporin-4 antibody-positive (AQP4-Ab+) neuromyelitis optica spectrum disorder (NMOSD) based on results of the primary treatment period (PTP) of CHAMPION-NMOSD, a phase 3, open-label, external placebo-controlled trial. Here, we report the final efficacy and safety results of CHAMPION-NMOSD (PTP and the long-term extension [LTE]). METHODS: Adult patients with AQP4-Ab+ NMOSD received an IV, weight-based loading dose of ravulizumab on day 1 and a maintenance dose on day 15 and every 8 weeks thereafter. After completion of the PTP (up to 2.5 years), patients could enter the LTE. The primary endpoint was time to first adjudicated on-trial relapse. The placebo group of the eculizumab phase 3 trial PREVENT was used as an external comparator because eculizumab availability at CHAMPION-NMOSD initiation precluded the use of concurrent placebo control. RESULTS: Of 58 patients enrolled in the trial, 56 entered and 55 completed the LTE. The overall median (range) follow-up was 170.3 (11.0-243.0) weeks, with 100.8 (53-137) weeks during the LTE. No patient receiving ravulizumab had an adjudicated on-trial relapse throughout the PTP (84.0 patient-years) and LTE (105.7 patient-years); relative reduction in risk of relapse vs placebo (n = 47) was 98.9% (95% CI 91.8-100; p < 0.0001). Treatment-emergent adverse events (TEAEs) and serious TEAEs were reported in 94.8% and 27.6% of patients, respectively, during the PTP and LTE. Most TEAEs were grade 1 and unrelated to ravulizumab. One patient discontinued ravulizumab because of TEAEs. Two cases of meningococcal infection occurred during the PTP; none occurred in the LTE. One death due to hypertensive heart disease (unrelated to ravulizumab) occurred during the LTE. DISCUSSION: Long-term ravulizumab treatment (median follow-up, >3 years) continued to show significant relapse risk reduction in patients with AQP4-Ab+ NMOSD, and the safety profile was consistent with the known safety profile for ravulizumab. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov, NCT04201262; EudraCT: 2019-003352-37. Submitted December 11, 2019. First patient enrolled: December 13, 2019. clinicaltrials.gov/study/NCT04201262. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that long-term ravulizumab treatment, as compared with placebo, decreases the probability of clinical relapse in patients with AQP4-Ab+ NMOSD.