OBJECTIVE: The purpose of this study was to evaluate gender differences in baseline measures of regional brain metabolism and to assess their reproducibility. METHOD: Fifteen male and 13 female healthy subjects, whose mean age was 44 years, were tested with positron emission tomography and [18F]fluorodeoxyglucose (FDG) under resting conditions; eight of the men and 11 of the women underwent a second FDG scan under the same conditions 4-6 weeks later to assess the reproducibility of the previous results. RESULTS: There were no differences in whole brain metabolism between the women and the men. In the first evaluation the female subjects showed significantly higher metabolism in the temporal poles and cerebellum than the male subjects. During the second evaluation the female subjects had significantly higher metabolism only in the cerebellum. CONCLUSIONS: This study documents significant and reproducible gender differences in cerebellar metabolism; their functional significance merits further evaluation.Abstract Teaser