This 24-week study will compare the safety and effectiveness of medication treatment alone (risperidone or aripiprazole) to medication treatment in combination with a parent management training program.

PDD can be a profoundly disabling condition across social, emotional, and academic domains. Safe and effective treatments for PDD are needed.

Participants are randomly assigned to receive either risperidone plus parent management training or risperidone alone for 24 weeks. Participants who show deterioration at Week 4 will be offered an alternative mediation treatment, aripiprazole. These participants will remain in their original treatment group (either med alone or med plus parent management training). After 6 months of treatment (Week 24), participants who respond to their treatment will be gradually discontinued from their medication treatment to learn if the response can be sustained without continued medication treatment (This phase of the study was ended in Nov. 2006) Adaptive and behavioral outcomes are assessed during the study.

Inclusion Criteria:

• Autistic Disorder, Asperger's Disorder, or Pervasive Developmental Disorder not otherwise specified
• Weight > 30 lbs
• IQ >= 35 or mental age of at least 18 months

Exclusion Criteria:

• Psychotic Disorder
• History of intolerance or nonresponse to risperidone
• Pregnancy
• History of neuroleptic malignant syndrome