Brain regions involved in tremor and voluntary movement were compared in seven subjects with hemiparkinsonian tremor using positron emission tomography and the [15O] water bolus activation method. Repeated measurements of the regional cerebral blood flow were performed both before and after tremor arrest induced by administration of L-dopa as well as during voluntary repetitive movements of the hand contralateral to tremor side. The normalized regional cerebral blood flow (NrCBF) was measured in regions of interest with anatomical boundaries that were defined for each subject by means of a three-dimensional reconstruction of magnetic resonance imaging data. Taking the rest after L-dopa as a control condition, NrCBF increased during tremor in a network of regions including the precentral (mean +/- SD 5.36 +/- 4.6%, P = 0.006) and paracentral (6.11 +/- 6%, P = 0.01) gyri contralateral to tremor side, the supplementary motor area (SMA; 4.03 +/- 4%, P = 0.02, n = 8 pairs), and the cerebellar vermis (8.64 +/- 9.9%, P = 0.01, n = 12). During voluntary repetitive movement of the hand contralateral to tremor compared with rest after L-dopa, the same patients activated the precentral (8.25 +/- 2.6%, P = 0.0006) and postcentral regions contralateral to movement (8.43 +/- 3.7%, P = 0.002), and the cerebellar cortex (3.49 +/- 2.1%, P = 0.03), precentral (3.58 +/- 3.1%, P = 0.04), and paracentral (4.03 +/- 3.6%, P = 0.04) regions ipsilateral to movement. The cerebellar vermis was activated (8.15 +/- 5.6%, P = 0.02, n = 8) as well as the SMA, but not significantly at the 0.05 level (5.16 +/- 5%, P = 0.08, n = 5). These results confirm the similarities of brain structures involved in parkinsonian tremor and voluntary movement and provide an anatomofunctional substrate for their clinical interactions.