A retrospective study was conducted in a clinic specialized in treating individuals with developmental disabilities to examine the effectiveness and tolerability of quetiapine in children and adolescents with pervasive developmental disorders. Ten consecutive outpatients (age = 12.0 ± 5.1 years) treated with quetiapine (dose = 477 ± 212 mg, duration = 22.0 ± 10.1 weeks) were identified and six were judged to be responders based on impressions from chart review and Conners Parent Scale (CPS). Improvements were observed in the conduct, inattention, and hyperactivity subscales of the CPS. Adverse events were mild with sedation being the most common, and no patient required treatment termination. Quetiapine may be beneficial in children and adolescents with pervasive developmental disorders, however open-label and double-blind, placebo-controlled studies are warranted.