This double-blind, multicenter study aimed to investigate the efficacy and safety of aripiprazole 10, 15 or 20 mg/day versus placebo. Patients requiring inpatient hospitalization for acute exacerbation of schizophrenia were randomized to once-daily aripiprazole 10, 15 or 20 mg/day or placebo for 6 weeks. The primary efficacy outcome was the mean change from baseline to Week 6 in the Positive and Negative Syndrome Scale (PANSS) Total score (last observation carried forward). Patients with no improvement by Week 3 (Clinical Global Impression-Global Improvement score > or =4) could transfer to open-label aripiprazole 20mg/day. In total, 420 patients were randomized to placebo (n = 108); aripiprazole 10 mg/day (n = 106); 15 mg/day (n = 106); or 20 mg/day (n = 100). Of these, 142 patients (34%) completed 6 weeks of treatment, 131 (31%) discontinued to receive open-label aripiprazole, and 147 (35%) for other reasons. Aripiprazole 10, 15 and 20 mg/day each showed significantly greater improvements from baseline than placebo for all efficacy measures, including PANSS Total, Positive and Negative scores, and the CGI-Severity of Illness score. Significantly greater improvements in PANSS Total score versus placebo were achieved by Week 1 with 10 or 20 mg/day and Week 3 with 15 mg/day. All three doses were well tolerated. Overall, aripiprazole was not associated with clinically meaningful differences in extrapyramidal symptoms, prolactin or weight changes versus placebo. Aripiprazole 10 mg/day is effective and well tolerated for patients experiencing an acute exacerbation of schizophrenia.