We describe the clinical characteristics, causes and response to treatment in 6 patients with AIDS who presented with abnormal movement disorders between January 1987 and July 1993 in our hospital, 3 with hemiballismus-hemichorea, 1 with athetosis, 1 myoclonia and 1 with "rubric" tremor. Brain imaging showed lesions in the corpus striatum in all the patients. Suspected diagnoses were cerebral toxoplasmosis in 4, cerebral lymphoma in 1 and progressive multifocal leukoencephalopathy in 1. The toxoplasmosis patients showed improvement (2 cases) or disappearance (2 cases) of movements with antiparasitic therapy. Treatment provided no benefit to the patients with leukoencephalopathy and lymphoma. Hemiballismus-hemichorea was the most common movement disorder in AIDS patients. The underlying cause is usually lesions in the basal ganglia arising from toxoplasmosis. If the lesions are so caused, movements may improve with antiparasitic therapy.