We studied 43 patients, aged 15 to 69 years, whose convulsive seizures were uncontrolled because the syndrome of juvenile myoclonic epilepsy was not recognized. Awakening myoclonic jerks appeared with tonic-clonic (18 patients), clonic-tonic-clonic (24 patients), and absence seizures (17 patients), with a mean age at onset of 13.6 years. Generalized seizures were present in relatives of 17 patients. All patients had diffuse 3 1/2- to 6-Hz multispike-wave complexes. Valproic acid stopped convulsions in 86% of patients. After being free of seizures for 2 years, withdrawal of valproic acid was followed by relapse of convulsions in 12 patients.