OBJECTIVES: To evaluate functional outcomes of aripiprazole once-monthly (ARI-OM) 400 mg (ARI-OM-400) versus a sub-therapeutic dose of ARI-OM (50 mg; ARI-OM-50), oral aripiprazole (ARI), and placebo, in two trials of stable patients with schizophrenia. METHODS: Detailed study designs have been reported previously. Results are reported for the double-blind, randomized phase of each study. ARI-OM is an extended-release injectable suspension given at 400 mg in the gluteal muscle. Functional outcome was measured using the Personal and Social Performance scale (PSP) and statistically analyzed using analysis of covariance with last observation carried forward. RESULTS: 403 patients were randomized to ARI-OM-400 (n=269) or placebo (n=134) in the first (246) trial. PSP scores at endpoint significantly worsened with placebo (-6.2) vs. ARI-OM-400 (-1.7; p=0.0002). In the second study (247), 662 patients were randomized to: ARI-OM-400 (n=265); ARI (n=266); or ARI-OM-50 (n=131). PSP scores with sub-therapeutic ARI-OM-50 significantly worsened (-2.39) vs. ARI-OM-400 (+0.45; p=0.03). Similar functional stability was observed with ARI (+0.08). CONCLUSIONS: Patient functioning, as assessed by PSP, was maintained with ARI-OM in both studies but deteriorated in patients randomized to either sub-therapeutic doses or placebo, confirming the benefits of adequately dosed antipsychotic therapy in preserving functional stability in long-term management of schizophrenia.