The authors investigated cognition in juvenile myoclonic epilepsy (JME), focusing on frontal functions as suggested by maximal spatial distribution of epileptiform activity seen over frontocentral regions. Fifteen patients with JME (mean age, 34.3 years; mean estimated IQ 101) were administered a battery of tests sensitive to frontal dysfunction. The number of patients with impaired test performance and the frequency of impairment per test were calculated. Performance on selected tests was compared with that of 15 patients with temporal lobe epilepsy (TLE) who were matched for estimated IQ using paired t-tests. Although the performance of the group with JME was not uniform--some patients showed marked impairment whereas others showed little or no deficit--a high frequency of impairment was found on tests of concept formation-abstract reasoning and mental flexibility, cognitive speed, and planning and organization. Significant differences were found between the group with JME and the group with TLE on tests requiring mental flexibility and concept formation-abstract reasoning. In conjunction with studies demonstrating intractable seizures in approximately 20% of patients, the results from this study suggest that JME is not a uniformly benign condition. Frontal deficits may have maladaptive behavioral consequences suggestive of personality dysfunction, as described anecdotally by previous investigators.