The aim of this study was to examine prospective outcomes in mentally retarded people with epilepsy seen for the first time during 1998 until the end of 2001. Two hundred and fourteen patients (120 men, 94 women, aged 11-70 years [median 34 years]) were referred over this 4-year period. Median duration of follow-up was 18 months (range, 13-36 months). Seventeen (8%) had nonepileptic attacks only, 10 of whom were being treated with antiepileptic drugs (AEDs). The remaining 197 (92%) patients had epilepsy, the majority (n=151, 77%) presenting with focal seizures. A total of 22 patients were started on AED treatment, with seizure freedom for at least a year being achieved in 10 (45%). AED manipulation was undertaken in a further 136 patients, resulting in 59 (43%) becoming seizure-free. No relationship was found between extent of mental retardation and seizure control. There was no deterioration in mean caregiver scores rating sleep, appetite, alertness, and behavior. These findings suggest that AED therapy can result in seizure freedom in more than 40% of mentally retarded people with epilepsy without producing unacceptable toxicity.