This phase III study evaluated the efficacy and safety of cariprazine, a dopamine D3 and D2 receptor partial agonist with preferential binding to D3 receptors, in patients with acute exacerbation of schizophrenia. Patients were randomized to 6-week double-blind treatment with placebo, cariprazine 3 to 6 mg/d, or cariprazine 6 to 9 mg/d. Primary and secondary efficacy: change from baseline to week 6 in Positive and Negative Syndrome Scale total and Clinical Global Impressions-Severity scores, respectively, analyzed using a mixed-effects model for repeated measures adjusting for multiple comparisons. Safety included treatment-emergent adverse events, clinical laboratory values, vital signs, electrocardiograms, ophthalmologic examination, Columbia-Suicide Severity Rating Scale, and extrapyramidal symptom scales. In the Safety Population (placebo, n = 147; cariprazine 3-6 mg/d, n = 151; cariprazine 6-9 mg/d, n = 148), 60.5% of patients completed the study. At week 6, statistically significant least squares mean differences in favor of cariprazine versus placebo were observed for Positive and Negative Syndrome Scale total score (3-6 mg/d: -6.8, P = 0.003; 6-9 mg/d: -9.9, P < 0.001) and Clinical Global Impressions-Severity (3-6 mg/d: -0.3, P = 0.012; 6-9 mg/d: -0.5, P < 0.001). Common treatment-emergent adverse events (≥5% and twice the rate of placebo) in both cariprazine groups were akathisia, extrapyramidal disorder, and tremor; most were mild to moderate in severity. Mean changes in metabolic parameters were generally small and similar between groups. Prolactin levels decreased in all groups. In conclusion, cariprazine 3 to 6 and 6 to 9 mg/d versus placebo demonstrated significant improvement on primary and secondary efficacy parameters. Cariprazine was generally well tolerated. These results suggest that cariprazine may be a new and effective treatment for schizophrenia.