Objective: To investigate the difference in the regional cerebral glucose metabolism between multiple system atrophy Parkinsonian type (MSA-P) and Parkinson's disease (PD). Material and methods: Fifteen patients with MSA-P, 32 patients with PD and eight cases of healthy control underwent positron emission tomography (PET) with F-18-fluorodeoxyglucose (F-18-FDG) showing glucose metabolism. Glucose metabolism ratios of various cerebral regions were compared as an indicator of regional cerebral glucose metabolic patterns. Results: The metabolism ratios of frontal lobe/occipital lobe, parietal lobe/occipital lobe, temporal lobe/occipital lobe and corpus striatum/occipital lobe in patients with MSA-P were lower than those in patients with PD and control, respectively (p<0.01). For patients with MSA-P, the metabolism ratio in thalamus was higher than those in lenticular nucleus and anterior cortical brain, respectively (p<0.01) and the changes of metabolism ratio in cortex, corpus striatum and thalamus were symmetric. For patients with PD, the metabolism ratio in corpus striatum was higher than that in thalamus and two side of the basal ganglia show asymmetric change of metabolism (p<0.01). Conclusion: This study suggests that significant differences exist in the patterns of regional cerebral glucose metabolism between MSA-P and PD. F-18-FDG PET might be a useful adjunctive method for differential diagnosis between MSA-P and PD.