The authors examined 65 patients with Alzheimer's disease for delusions and explored the relationship of delusions with regional cerebral glucose metabolism determined by [18F]fluorodeoxyglucose PET. In patients with delusions (n = 26), normalized glucose metabolism was significantly increased in the left inferior temporal gyrus and significantly decreased in the left medial occipital region as compared with those without delusions (n = 39). The two groups were similar in age, sex, and dementia severity. These results suggest that delusions in Alzheimer's disease are attributable to a dysfunction in specific brain areas rather than a simple reaction to intellectual deficits.