The study period is a 9-week, acute treatment phase. Patients who meet inclusion criteria will receive aripiprazole for 8 weeks. Treatment will be initiated with 2.5 mg/day at the baseline visit, 5 mg/day aripiprazole for the first week and flexibly titrated up to a maximum of 30 mg/day over the next six weeks. Patients will be seen weekly for the first three weeks of this phase of treatment, and then at 2-week intervals for the remainder of the study.