Inclusion Criteria:

• Signed written informed consent
• Men and women, ages 18 to 65. Women of childbearing potential (WOCBP) must be using an adequate method of contraception to avoid pregnancy throughout the study in such a manner that the risk of pregnancy is minimized.
• Patients who have not been hospitalized during last three months
• Patients who have kept clinically stable dosage during last one month
• Patients with a diagnosis of schizophrenia and schizoaffective disorder as defined by DSM-IV criteria
• Patients whose symptoms are not optimally controlled or whose antipsychotic medication is not well-tolerated, which in the clinical judgment of the treating psychiatrist require a change of treatment.
• Patients who have received antipsychotics in the past must have shown a response to a neuroleptic medication other than clozapine.

Exclusion Criteria:

• Patients who are unwilling or unable to use an acceptable method to avoid pregnancy for the entire study period
• Women who are pregnant or breastfeeding
• Patients who are at risk for committing suicide: either having active suicidal ideation considered clinically significant or recently attempted suicide
• Patients with a diagnosis of bipolar disorder, depression with psychotic symptoms, or organic brain syndromes
• Patients who have met DSM-IV criteria for any significant Psychoactive Substance Use Disorder within the 3 months prior to Screening
• Patients considered treatment-resistant to antipsychotic medication (patients need to have shown a previous response to a antipsychotic medication other than clozapine) and patients with a significant history of intolerance to multiple antipsychotic treatments
• Treatment with a long-acting antipsychotic (i.e., haloperidol decanoate or fluphenazine decanoate) in which the last dose was within 3 weeks of randomization.
• Patients with a history of neuroleptic malignant syndrome
• Patients with epilepsy, a history of seizures (except for a single childhood febrile seizure), or a history of an abnormal EEG, severe head trauma, or stroke or who have a history or evidence of other medical conditions (e.g., congestive heart failure) that would expose them to an undue risk of a significant adverse event or interfere with assessments of safety or efficacy during the course of the trial
• Patients who would be likely to require prohibited concomitant therapy during the trial
• Patients who have previously enrolled in an aripiprazole clinical study or who have participated in any clinical trial with an investigational agent within the past month
• Prisoners or subjects who are compulsorily detained for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled into this study.