Different aspects of anticonvulsant treatment and psychopathology were studied in a group of 150 adult epileptic mentally handicapped patients and compared with a matched control group of 150 adult non-epileptic mentally handicapped people. Patients were collected from both hospital and community. Most epileptic patients received monopharmacy of the modern generation of anticonvulsant's within the British National Formulary recommended dosage schedule. Most had their serum anticonvulsant level within the local laboratory reference range. Anticonvulsant's other than sodium valproate lowered serum folate level. In general there was no direct relationship with anticonvulsant medication and psychopathology, although carbamazepine monopharmacy showed come protective effect on aggressive behaviour.