The aim of this study was to evaluate the safety and tolerability of aripiprazole once-monthly (ARI-OM) for the maintenance treatment of schizophrenia. This long-term, pivotal study had four phases: oral conversion (phase 1, 4–6 weeks); oral stabilization (phase 2, 4–12 weeks); ARI-OM stabilization with coadministration of oral aripiprazole in the first 2 weeks (phase 3, 12–36 weeks); and a 52-week, randomized [phase 4, ARI-OM vs. placebo (2 : 1)], double-blind, maintenance phase. Safety was assessed across study phases by the time of first onset of adverse events, as were objective measures of extrapyramidal symptoms, fasting metabolic parameters, and body weight. Patient enrollment was phase 1=633; phase 2=710, of whom 210 entered phase 2 directly; phase 3=576; and phase 4=403 (ARI-OM, n=269; placebo, n=134). Adverse events (>5%) in any phase were insomnia, headache, anxiety, akathisia, increase in weight, injection-site pain, and tremor. Headache, somnolence, and nausea had a peak first onset within 4 weeks of treatment initiation. The incidence of extrapyramidal symptoms was similar in all phases. There were no unexpected changes in weight or shifts in fasting metabolic parameters across all study phases. ARI-OM had a safety and tolerability profile comparable with oral aripiprazole in maintenance treatment of schizophrenia.