The objective of this study was to examine long-term adverse events of risperidone in 19 children, adolescents, and adults with Pervasive Developmental Disorders and intellectual disability, continuing risperidone for a mean of 186.5 weeks, following a 46-week risperidone study. Nineteen individuals continued long-term follow-up after our published risperidone placebo-crossover acute study (22 weeks) and 24-week maintenance phase on 40 participants. Long-term ratings included the Dyskinesia Identification Systems Condensed User Scale and Neuroleptic Side Effects Checklist. Weight and prolactin levels were also measured. A range of significant neurological side effects occurred: akathisia in 10%, 2 individuals developed tardive dyskinesia, 1 developed oculogyric crisis; withdrawal dyskinesia occurred in 2 of 9 individuals discontinuing risperidone. All 10 children and adolescents continued greater than 7% weight gain. Adults gained less weight, but 2 developed Type 2 diabetes. Prolactin (PRL) elevation continued in all 7 patients with PRL measures but normalized in 2 individuals after aripiprazole addition. Movement side effects were significant. Children and adolescents continued greater than 7% weight gain; PRL elevation continued. (Contains 3 tables.)