We estimated regional and global metabolic rates for glucose using 18F-fluorodeoxyglucose (FDG) and PET in six patients with hemiparkinsonism-hemiatrophy syndrome (HPHA; mean age, 41.0 +/- 12.4 years). We used 18F-fluorodopa (FDOPA) and PET in two patients to quantify presynaptic nigrostriatal dopaminergic function. We compared measures of brain glucose metabolism and striatal FDOPA uptake with those calculated for 10 age-matched normal volunteers (mean age, 35.1 +/- 8.0 years) and 10 patients with typical unilateral Parkinson's disease (unilat-PD; mean age, 58.2 +/- 13.8 years). All six HPHA patients demonstrated significant metabolic reductions (> 3 SD) in the contralateral basal ganglia or frontal cortex as compared with normal control values. Mean normalized glucose metabolism was reduced in the contralateral caudate and lentiform nuclei (p < 0.005) as compared with that in unilat-PD and normal controls. In both patients studied with FDOPA, contralateral striatal uptake was significantly reduced (> 3 SD) as compared with normal control values. These results suggest that the clinical manifestations of HPHA arise through a combination of pre- and postsynaptic nigrostriatal dopaminergic dysfunction. FDG and PET may be useful in differentiating this disorder from typical unilat-PD.