The aim of our study was to evaluate the effectiveness of ethosuximide in the treatment of epileptic negative myoclonus, a motor disorder that can occur in childhood partial epilepsy. We introduced ethosuximide in nine patients with partial epilepsy of varying etiology (idiopathic, cryptogenic, symptomatic) who presented with epileptic negative myoclonus. The drug was added to the patients' preexisting antiepileptic drugs, which were maintained unchanged for the following 6 months. Epileptic negative myoclonus disappeared in all patients 15 to 30 days after ethosuximide was started. Plasma ethosuximide levels ranged from 55 to 89 micrograms/mL. The clinical response was not influenced by the patients' preexisting treatment or by the etiology of the epilepsy. No side effects were observed, and none of the patients presented a recurrence of epileptic negative myoclonus during follow-up. Furthermore, in five patients we observed the disappearance of partial seizures; in the remaining patients seizures were reduced by more than 75%. Electroencephalograms showed a decrement or disappearance of focal paroxysmal abnormalities. Our results suggest that ethosuximide is effective in the treatment of epileptic negative myoclonus and that it should be considered as a first-choice drug in the treatment of this motor disorder.