The authors report an open clinical trial of clomipramine for chronic stereotypic and self-injurious behaviors in 11 consecutive patients with concomitant developmental disorders. Ten patients (91%) had marked decreases in rates of target behaviors. No seizures occurred despite the inclusion of six patients with previous histories of epileptic events, and improvement was evident regardless of level of mental retardation. These findings support both the clinical use of serotonergic medications in this population and the need for further research.