This study was performed to show the usefulness of N30 and N20 of median nerve SSEPs for evaluating the pathogenesis of central nervous system movement disorders. The subjects were 14 patients, consisting of 7 patients with an extrapyramidal lesion, 3 patients with suspicion of hypoxic-ischemic cerebral injury before birth period (H-I group), 3 patients with kernicterus during the neonatal period (kernicterus group), and 1 patient having Wilson's disease. Seven patients had spastic hemiplegia. Patients with athetotic CP had the ability to handle an electric wheelchair alone, and those with spastic hemiplegia could walk alone. Thirty control subjects were included in this study for clinical investigation. The characteristic finding of a predominant absence or amplitude reduction of frontal N30 compared with that of parietal N20 (4 and 1, respectively, out of 6 examinations) was obtained in athetotic CP patients of the H-I group. The predominant absence of N30 compared with N20 did not appear in the kernicterus group, hemiplegic patients or a patient with Wilson's disease. Therefore, frontal N30 might sensitively reflect destructive damage in the frontal basal ganglia in children.