Research into the pharmacotherapy of autistic disorder has steadily increased over the past two decades. Several psychoactive medications have shown efficacy for selected symptoms of autistic disorder and can be used to augment critical educational and behavioral interventions that are the mainstays of treatment. A comprehensive review of medication trials conducted in individuals with autistic disorder and other pervasive developmental disorders is presented. The typical antipsychotic haloperidol is the best-studied medication in autistic disorder but is associated with a high rate of dyskinesias. Investigations to date suggest that the atypical antipsychotics such as risperidone have efficacy for certain symptoms of autistic disorder and may be better tolerated than typical antipsychotics. Preliminary results from trials with serotonin-reuptake inhibitors are favorable, although efficacy has not been demonstrated in younger age groups. Recent controlled studies of naltrexone suggest that the drug has minimal efficacy. In two small controlled investigations, clonidine was more effective than placebo for a variety of symptoms, including hyperactivity and irritability; in one of these studies, however, the majority of patients relapsed within several months. Psychostimulants reduced hyperactivity and irritability in one small double-blind crossover study in children with autistic disorder, although these agents are frequently reported to exacerbate irritability, insomnia, and aggression in clinical populations. Recent controlled trials of secretin have not shown efficacy compared to placebo. Several other medications, including buspirone, mood stabilizers, and g -blockers, have produced symptom reduction in some open-label studies and may warrant controlled investigation.