Levetiracetam is a new antiepileptic agent that exerts antimyoclonic effects. We conducted an open-label trial to evaluate the effect of levetiracetam in chronic cortical myoclonus of diverse etiologies and to determine whether levetiracetam affects electrophysiological findings. Sixteen patients, aged between 19 and 72 years, with refractory, chronic, cortical myoclonus were recruited. We assessed myoclonus severity with the Unified Myoclonus Rating Scale (UMRS). The electrophysiological study comprised jerk-locked averaging, somatosensory evoked potentials (SEPs), and long loop reflex I. Levetiracetam was administered add-on at a starting dose of 500 mg twice per day up to the target dose of 50 mg/kg/day. Patients were reevaluated clinically and electrophysiologically 2 weeks after the titration phase. Fourteen patients completed the trial. Posttreatment UMRS scores showed an improvement of myoclonus in all cases. Pretreatment, 9 patients had "giant" SEPs. Posttreatment, the amplitude of these SEPs was reduced by more than 50% in 3 of 9 patients, and the mean N20-P25 amplitude was reduced significantly. Pre- and posttreatment SEP amplitude was not related to myoclonus severity or duration. Levetiracetam is a promising and a relatively easy-to-test antimyoclonic agent, which has the potential to improve significantly the patient's disability; however, its long-term efficacy should be verified in larger controlled studies.