In this study, motor unit number estimate (MUNE) analysis with McComa's technique was used to detect any change in lower motor neuron count in juvenile myoclonic epilepsy (JME). The study included 10 JME patients, 8 idiopathic generalized epilepsy (IGE) patients, 7 patients with mesial temporal sclerosis (MTS), and 15 normal subjects. All the patients and normal subjects were subjected to MUNE analysis on the abductor pollicis brevis and tibialis anterior muscles, as well as needle electromyography and nerve conduction studies. Electromyographic and nerve conduction studies were normal in all groups. MUNEs in the JME group and were significantly lower than those of normal subjects (P < 0.001). MUNEs of IGE and NITS patients also tended to be lower than that of normal subjects with no significant difference from normal subjects. MUNEs of abductor pollicis brevis and tibialis anterior muscles were 114 +/- 24 and 90 +/- 15 for normal subjects, 59 +/- 18 and 50 +/- 23 for JME patients, 91 +/- 22 and 75 +/- 19 for IGE patients, and 84 +/- 42 and 80 +/- 29 for MTS patients respectively. It may be reasonable to suggest that a genetic origin is responsible for a tendency to contract epilepsy, and the disorganization of lower motor neurons may be shared in JME.