Study of Aripiprazole in the Treatment of Children and Adolescents With Autistic Disorder (AD).

Inclusion Criteria: * Meets current Diagnostic and Statistical Manual for Mental Disorders-Fourth Edition (DSM-IV) diagnostic criteria for AD and demonstrates serious behavioral problems. Diagnosis confirmed by Autism Diagnostic Interview- Revised (ADI-R) * CGI score \> = 4 AND and Aberrant Behavior Checklist (ABC) Irritability/Agitation subscale score \> = 18 at screening and baseline (randomization) * Mental age of at least 18 months * Male or female 6 to 17 years of age, inclusive, at the time of randomization Exclusion Criteria: * Patients considered treatment resistant to neuroleptic medication based on lack of therapeutic response to 2 different neuroleptics after treatment of at least 3 weeks each. * Patients previously treated and not responding to aripiprazole treatment * The patient is currently diagnosed with another disorder on the autism spectrum, including PDD-NOS, Asperger's Disorder, Rett's Disorder, Fragile-X Syndrome or Childhood Disintegrative Disorder * Current diagnosis of bipolar disorder, psychosis, or schizophrenia, or major depression * A seizure in the past year * History of severe head trauma or stroke * Patients undergoing non-pharmacologic therapies (e.g., psychotherapy, behavioral modification) must have started at least 2 months prior to the initial screening visit and must remain in a consistent treatment program for the duration of the study.