Children with autism and the related PDDs may benefit from serotonin reuptake inhibitors such as clomipramine, fluoxetine, fluvoxamine, and sertraline for targeting repetitive thoughts and behaviors, anxiety, and depressed mood. To date, however, there are few controlled studies of these agents in children with PDD, so definitive evidence is lacking. Despite preliminary results in favor of naltrexone, neuroleptic medication appears to be effective for reducing aggression, self-injurious behavior, agitation, and stereotypies. The primary drawback with traditional neuroleptics is risk of short- and long-term side effects. The newer atypical neuroleptics have the potential for benefit with fewer extrapyramidal side effects, but more study is needed to establish their efficacy and safety. Children on neuroleptic medications should be started at the lowest possible dose, with gradual increases until clinical benefit is observed. The likelihood of untoward side effects is increased if the medication dose is increased rapidly. Baseline measurement of target behaviors can be aided by using standardized scales. The presence of abnormal movements should be assessed before initiating treatment and at regular intervals during the course of treatment--including after medication withdrawal. Weight gain is emerging as a recurrent side effect with the atypical neuroleptics. Thus, weight should be monitored, and the family should be advised about a diet baseline. As with all treatments of children with severe behavioral difficulties, pharmacotherapy should be instituted in the context of an integrated treatment plan.