Risperidone has proven efficacy with reduced likelihood of causing extrapyramidal symptoms in the treatment of schizophrenia. Initial work suggests its utility in the management of aggression and self injury in patients with mental retardation. The use of risperidone in eight adult patients with moderate to profound mental retardation is described. Risperidone in these individuals was associated with significant reduction in aggression and self injurious behavior. Side effects were primarily those of sedation and restlessness. These cases illustrate the possible utility of risperidone in the treatment of aggression and self injury in adult patients with moderate to profound mental retardation.