Regional cerebral blood flow was measured using H2(15)O and positron emission tomography in a group of 6 patients with idiopathic torsion dystonia and in a group of 6 control subjects. Subjects were scanned while at rest and when performing paced joystick movements in freely chosen directions with the right hand. Patients with idiopathic torsion dystonia showed significant overactivity in the contralateral lateral premotor cortex, rostral supplementary motor area, Brodmann area 8, anterior cingulate area 32, ipsilateral dorsolateral prefrontal cortex, and bilateral lentiform nucleus. Significant underactivity was found in the caudal supplementary motor area, bilateral sensorimotor cortex, posterior cingulate, and mesial parietal cortex. These results are consistent with inappropriate overactivity of striatofrontal projections and impaired activity of motor executive areas in idiopathic torsion dystonia and may explain the simultaneous dystonic posturing and bradykinesia evident in these patients.