Abstract Regional cerebral metabolic rate of glucose (rCMRglc) was studied in 19 patients with a clinical diagnosis of dementia with Lewy bodies (DLB) and 19 patients with a clinical diagnosis of Alzheimer's disease (AD), using [ 18F]fluorodeoxyglucose ([ 18F]FDG) and positron emission tomography (PET). The two groups were matched with age, gender, disease duration and severity of cognitive disturbances. In `dementia with Lewy bodies' (DLB) patients, when compared with AD patients, significant rCMRglc decreases were distributed in the temporo-parieto-occipital association cortices and the cerebellar hemispheres. In contrast, the medial temporal and cingulate rCMRglc were significantly lower in AD patients than those in DLB patients. These different regional emphases of glucose hypometabolism are consistent with the pathological and neurochemical differences between DLB and AD and explain the different clinical features of the two diseases.