Atypical Neuroleptic Drugs in People With Mental Retardation/Developmental Delay

Inclusion Criteria * Primary diagnosis of mental retardation (IQ \< 70) * Scheduled for medication reductions from psychotropic drugs and subsequent placement on risperidone * Severe self-injury, aggression, property destruction, or stereotypic behavior for 6 months prior to study entry * No seizures, or seizures under control of medication for previous 2 years Additional Inclusion Criteria for Substudy * Participants in the primary study who are available for 2 hour weekly or bi-weekly clinic visits and are able to have observers in their home, school, and/or work environment Exclusion Criteria * Degenerative disease that may affect motor or cognitive functioning * Progressive disease of an organ system * Advanced age that may produce deteriorating cognitive or motor functioning * Multiple sensory or motor disabilities that will interfere with seeing the stimuli and responding to the computer