Ninety-nine mentally retarded, brain damaged, epileptic patients were treated for as long as six months will sulthiame, a new type of chemical agent that has been reported by others to possess anticonvulsant properties. Patients were divided into 3 groups on the basis of the frequency of seizures. Sulthiame was added to other anticonvulsants that the patients were receiving, but these drugs were gradually eliminated whenever possible, particularly in those patients whose seizures were well controlled. When used in combination with other anticonvulsants, sulthiame was noted to reduce the frequency of seizures in patients with poorly controlled seizures. It was usually tolerated in a dosage of 8 to 11 mg. per kilogram of body weight and was more effective in patients with mild diffuse dysrhythmias or focal abnormalities than in those with paroxysmal disorders as determined by electroencephalography. Lethargy, anorexia, and ataxia were noted in 52 patients and these side effects may limit the usefulness of sulthiame.