Regional and global metabolic rates for glucose were estimated using 18F-fluorodeoxyglucose and positron emission tomography in 10 patients with a clinical likelihood of striatonigral degeneration (2 men and 8 women; mean age, 61.8 ± 6.9 years; mean disease duration, 4.7 ± 2.2 years; mean Hoehn and Yahr score, 3.5 ± 0.8). Measures of brain glucose metabolism in these patients were compared with those for 10 age-matched normal volunteers, 10 disease severity–matched patients with Parkinson's disease(PD), and 10 disease duration–matched patients with PD. Normalized glucose metabolism was significantly reduced in the caudate(p < 0.03) and putamen (p < 0.003) as compared with that in normal and PD control subjects, and discriminated patients with striatonigral degeneration from control subjects (p < 0.002). Putamenal hypometabolism in patients with striatonigral degeneration correlated significantly with quantitaive ratings of motor disability (p < 0.02). These results suggest that quantitative 18F-fluorodeoxyglucose positron emission tomography techniques may be useful in supporting a diagnosis of striatonigral degeneration in life, and in objectively assessing disease severity and potential therapeutic interventions.