Prevalence rates of epilepsy are much higher among persons with developmental disabilities compared to the general population. Anticonvulsant medication is the most common method of treating seizure disorders. Many of these antiepileptic medications (AEDs) are associated with various side effects, which may have detrimental effects on the social skills of those with developmental disabilities. The present study investigated the effects of AEDs on the social skills of individuals with mental retardation (MR) residing in an institutional facility. The social skills of 130 individuals were assessed by the Matson Evaluation of Social Skills for Individuals with sEvere Retardation (MESSIER). Sixty-five of these individuals were diagnosed with a seizure disorder and received only one AED at the time of this study. These individuals were taking one of three AEDs (carbamazepine, valproic acid, or phenytoin). Participants belonging to one of these three medication groups were matched with residents for age, gender, level of MR and race, who did not have seizures or receive AEDs. MESSIER scores of each medication group were compared to its respective control group. Those individuals receiving phenytoin presented less positive social skills than their matched counterparts in the phenytoin-control group.