The use of psychostimulants in autistic disorder has not received extensive evaluation. Furthermore, their use for the symptomatic control of autistic disorder has been felt to be contraindicated. This study investigates the use of methylphenidate (MPH) for the treatment of selected symptoms of autistic disorder. Ten children, ages 7-11, with a DSM-III-R diagnosis of autistic disorder participated in a double-blind crossover study using placebo and two MPH doses (10 mg or 20 mg bid). Subjects showed modest but statistically significant improvement on MPH over placebo. No significant side effects including worsening stereotypic movements occurred on either dose. Improvement in hyperactivity and lack of adverse effects suggest that MPH may be useful in the treatment of hyperactive autistic children.