Our objective was to study the short-term efficacy and safety of methylphenidate in patients with the dual diagnosis of cerebral palsy and attention-deficit hyperactivity disorder (ADHD). Twenty-nine patients (8.0 +/- 4.0 years old) with cerebral palsy and ADHD completed the study. In a prospective, crossover, double-blind paradigm, patients were treated with methylphenidate or placebo, each for 4 weeks. Parents and teachers completed a modified Abbreviated Conners' Rating Scale at the beginning of the study and the end of the first and second months of treatment with methylphenidate or placebo. Parents were contacted weekly to report side effects. Methylphenidate treatment, as assessed by teachers' ratings, resulted in a significant improvement in ADHD symptomatology (t = 2.29, df = 27, P < .05); however, a trend for improvement was noted only on the parents' ratings. After the conclusion of the study, 12 patients continued methylphenidate for 20 +/- 10 months. Side effects were minimal, with the exception of transient hallucinations in one patient. In children with cerebral palsy and ADHD, methylphenidate is effective, rendering it a valuable adjunct to their overall medical therapy.