A case of paroxysmal kinesigenic choreoathetosis (PKC) was described. The patient had attacks of paroxysmal choreoathetotic movements lasting 20-30 seconds. The attacks were regularly precipitated by sudden and unintentional movements. There were no metabolic abnormalities. EEG showed no epileptiform discharges. The attacks were subsided after administration of carbamazepine. We studied this patient with single photon emission computed tomography (SPECT) using 99mTc-HMPAO. Ictal SPECT revealed decrease of cerebral blood flow in the basal ganglia on the contralateral side of choreothetotic movements. Although the pathophysiology of PKC is still uncertain, it is hypothesized that motor activities are influenced by the direct pathway (positive feedback) and the indirect pathway (negative feedback) from the basal ganglia to the motor cortecis. Dysfunction of negative feedback is considered to be common underlying mechanisms of hyperkinetic disorders. Our findings support this hypothesis. Dysfunction of basal ganglia is likely relevant to the genesis of choreoathetosis.