Clinical and electroencephalographic data and response to drug therapy of 3 boys and 3 girls aged 14-19 years, mean 16, with juvenile myoclonic epilepsy (JME) are described. All presented with violent myoclonic jerks upon awakening, prompted by sleep deprivation and precipitated by deliberate awakening. Following onset of myoclonic jerks, generalized tonic-clonic seizures (GCTS) and absences occurred after 6-18 months (mean 11). The EEG revealed normal background activity in all, along with generalized epileptiform activity in the form of 3-4 Hz polyspike/slow wave or spike/slow wave, commonly induced by hyperventilation. Valproic acid (VPA), 12 mg/kg/day (range 10-15), resulted in complete and rapid cessation of myoclonic jerks, of absences and recurrent GTCS. Discontinuation of VPA resulted in recurrence of myoclonic jerks and then GTCS, but were completely controlled by reinstitution of VPA. All have remained asymptomatic on VPA, with cognition preserved, during a follow-up of up to 6 years. JME is a unique, benign, epileptic syndrome easily and rapidly controlled by rather small doses of valproic acid given on a long-term basis. Myoclonic jerks may serve as a reliable indicator of JME and therefore should be screened for in any case of unprovoked generalized seizures. The smallness of the doses of the drug used suggests that the dose prescribed should be "syndrome" related rather than weight related, as is usually prescribed in children.