The findings provide preliminary support for the effectiveness of olanzapine in treating agitation and aggression among adolescents with subaverage intelligence and a pattern of disruptive behavior. Ten of fifteen subjects showed at least a fifty-percent decrease in these behaviors from the start of the treatment. In addition to improvement in agitation and aggression, associated problems of overactivity, inattention, and impulsivity also improved. Many subjects responded to relatively moderate doses of olanzapine. Two subjects were prematurely dismissed from the study because of a worsening of problem behaviors, and two were dismissed because of side effects. The remaining subjects experienced a range of side effects, most of which were transient, with the exception of weight gain. Despite the weight gain, most families chose to continue with the medication trial as long as there were observed behavioral improvements. The authors advise that future double-blind, placebo-controlled studies should confirm these findings and assess long-term safety and outcomes. Sixteen adolescents (ages 13-17) with borderline to moderate mental retardation and patterns of disruptive behavior were enrolled in this eight-week olanzapine trial (5-20 mg/day). Measures used to determine effects were the Aberrant Behavior Checklist, Conners Parent Rating Scale, Clinical Global Impressions, and two side-effects scales. 3 tables and 27 references