Hemichorea and hemiballism have been considered dèbilitating and irreversible disorders. Eight patients with vascular hemichorea were treated with perphenazine. All were elderly and hypertensive. Three had primarily choreic movements while five had, in addition, proximal flailing movements of hemiballism. In seven, dramatic response to perphenazine therapy was seen, with virtual cessation of movements. In one case, only partial response was obtained with a high dose of perphenazine, and this dose had to be reduced because of drowsiness and hepatotoxicity. In four patients, movement did not recur after the drug was stopped. This study indicates that perphenazine can be a highly effective agent for the treatment of hemichorea and hemiballism and that improvement can be maintained in some patients even after therapy is discontinued.