We analyzed the somatosensory evoked potentials (SEP) of 35 patients with juvenile myoclonic epilepsy (JME), 26 patients with idiopathic generalized epilepsy (IGE), and a control group consisting of 24 healthy people. The N19-P25 interval was significantly prolonged in the IGE group both as compared with the JME and control groups. This finding may be related to antiepileptic drug (AED) treatment, principally phenytoin (PHT). No differences were noted in N19 amplitude in any group. The P25 and N33 amplitudes were significantly higher in the JME group. In 5 patients of the JME group (14%) "giant SEP" were observed, but no differences were evident in the electroclinical characteristics with respect to the other JME patients. JME is one of the causes of giant-SEP.