Evaluating the Effectiveness of Aripiprazole and D-Cycloserine to Treat Symptoms Associated With Autism

Inclusion Criteria: * Weight of at least 15 kg (33.75 lbs) * Meets DSM-IV criteria for autistic disorder * Outpatient * Medication-free for at least 2 weeks prior to baseline for all psychotropic medications. More information about this criterion, including exceptions, can be found in the protocol. * Clinical Global Impression Scale Severity score (CGI-S) of at least 4 * Irritability subscale of the Aberrant Behavior Checklist (ABC) score of at least 18 * An IQ of at least 35 or a mental age of at least 18 months * In good physical health Exclusion Criteria: * Meets DSM-IV criteria for Asperger's disorder, Rett's disorder, childhood disintegrative disorder, any other pervasive developmental disorder (PDD), schizophrenia, psychotic disorder, or bipolar disorder * Current or past history of alcohol or other substance abuse within 6 months of study entry * Comorbid neurodevelopmental disorder with possible association to autism (e.g., fragile-X syndrome, tuberous sclerosis) * A significant medical condition such as heart, liver, kidney, or lung disease, or a seizure disorder * Pregnant * Prior adequate use of aripiprazole. More information about this criterion can be found in the protocol. * Evidence of hypersensitivity to aripiprazole * History of neuroleptic malignant syndrome