Children and adolescents with obsessive compulsive disorder were studied in an 8-week, multicenter, double-blind, parallel groups trial of clomipramine hydrochloride (CMI) versus placebo. Efficacy assessments included the child version of the Yale-Brown Obsessive Compulsive Scale and the National Institute of Mental Health Global rating scale. At the end of 8 weeks, CMI-treated patients showed a mean reduction in Yale-Brown Obsessive Compulsive Scale score of 37% compared to 8% in the placebo group. Side effects were typical of tricyclic antidepressants. In a 1-year open label treatment, CMI continued to be effective and well tolerated.