Aripiprazole is a new psychotropic agent that possesses a unique pharmacologic profile. The drug demonstrates partial dopamine agonist activity and has been labeled a third-generation antipsychotic and dopamine system stabilizer. We report on the use of aripiprazole in the treatment of maladaptive behaviors in three individuals (cases) with mental retardation. Three adolescents (two was (were) diagnosed as mental retardation and pervasive developmental disorder, one was diagnosed as mental retardation) received an open-label trial of aripiprazole with 5 to 10 mg/day. Drug response was evaluated by using the Aberrant Behavior Checklist, Conners Parent Rating Scale and Clinical Global Impressions- Improvement Scale first month after treatment. Side effects were followed by UKU Side Effect Rating Scale. Aripiprazole was well tolerated and somehow effective in all of the cases and appears to be a safe and efficacious alternative in the management of patients with both intellectual disabilities and pervasive developmental disorders. Only one of the patients was taken as treatment responder according to definition, the other two also had a slight improvement in clinical sense. Though short duration of treatment and relatively lower drug doses these results with aripiprazole indicate a probable treatment option in this difficult-to-treat population. Clinical studies are needed to clarify the effectiveness and safety of this medication.