Risperidone (Risperdal), a psychotropic atypical antipsychotic agent, is thought to act via dopamine D(2) and serotonin (5-HT [5-hydroxytryptamine])(2A) receptor antagonism. The clinical efficacy of oral risperidone in the treatment of bipolar mania and schizophrenia in adult patients is well established. In the US, risperidone is also approved for the treatment of irritability associated with autistic disorder in children and adolescents aged 5-16 years, for the treatment of schizophrenia in adolescents aged 13-17 years and, as monotherapy, for the short-term treatment of acute manic and mixed episodes associated with bipolar I disorder in children and adolescents aged 10-17 years. Oral risperidone treatment was better than placebo treatment in reducing irritability and other behavioral symptoms associated with autistic disorder in children and adolescents in two well designed short-term trials, with these benefits maintained in those receiving risperidone for up to 6 months. The drug had a clinically manageable tolerability profile, with most adverse events being of mild to moderate intensity. There are some aspects of treatment, such as weight gain, somnolence, and hyperglycemia, that require monitoring, and the long-term safety of risperidone in children and adolescents with autistic disorder remains to be fully determined. With these issues in mind, risperidone offers a valuable emerging option for the treatment of irritability associated with autistic disorder in children and adolescents.