OBJECTIVE Extraversion, a trait associated with individual differences in approach motivation and the experience of positive emotional states, is negatively correlated with certain psychiatric disorders, including depression and social phobia. The authors examined the correlation between extraversion and regional cerebral blood flow (rCBF) while participants were exposed to olfactory stimuli in order to further characterize individual differences in hedonic processing associated with this trait. METHOD Twelve healthy participants were exposed to pleasant and unpleasant odors while rCBF was measured using [(15)O] water PET. The NEO Five-Factor Inventory was used to assess extraversion. Associations between extraversion scores and rCBF in each olfactory stimulus condition were assessed by correlational analysis. RESULTS During the pleasant smell condition, extraversion was correlated with rCBF in the amygdala and occipital cortex. During the unpleasant smell condition, extraversion was correlated with rCBF in the occipital cortex and inferior temporal gyrus. CONCLUSIONS These results provide important evidence for the biological basis of extraversion and indicate that there are systematic individual differences in patterns of brain activation in response to affective stimuli.