During the Screening Period, subjects can be treated with any oral antipsychotic medication of the clinician's choice, with the exception of clozapine and olanzapine. However, oral olanzapine is permitted during the Screening Period only for subjects who are eligible for Phase A. Following the Screening Period, subjects who have no history of aripiprazole use will be entered into Phase A, the Oral Tolerability Phase. Subjects from Phase A that demonstrate tolerability to aripiprazole will then be entered into Phase B (i.e., the Treatment Phase). Subjects who already have a history of tolerating at least three consecutive oral doses of aripiprazole will be entered directly into Phase B. All eligible subjects will eventually enter Phase B.