This study investigated the efficacy and tolerability of potassium bromide in 113 patients (aged, 1-20 years) with severe epilepsy and generalized tonic-clonic seizures. Potassium bromide was started at 45 mg/kg and raised to 70 mg/kg (median). Steady-state blood level was reached after a median of 28 days (range, 5-95 days). The number of patients who had suffered generalized tonic-clonic seizures during the last month dropped from 82 to 41, and the median frequency, dropped from 4.5 to 0 per month. Of the patients with generalized tonic-clonic seizures during baseline, 49% showed none in the last 4 weeks of the study, and another 31% showed a reduction by more than 50%. Potassium bromide should have a place as a drug of tertiary choice in the treatment of children with epilepsy. Experience with the drug and close clinical and pharmacologic monitoring are necessary to achieve the greatest possible benefit and avoid side effects.