Objective: Although the brain areas involved in emotional response and in the recognition of others' emotions have been reported, the neural bases of individual differences in affective style remain to be elucidated. Alexithymia, i.e., impairment of the ability to identify and communicate one's emotional state, influences how emotions are regulated. Alexithymia has been hypothesized to involve anterior cingulate dysfunction. Therefore, the authors searched for differential cerebral regional activation in response to emotional stimuli in subjects with alexithymia. Method: Two groups of eight men each were selected from 437 healthy subjects on the basis of high or low scores on the 20-item Toronto Alexithymia Scale. Using functional magnetic resonance imaging (fMRI), the authors compared the two groups for their regional cerebral activation in response to the presentation of pictures with validated positive or negative arousal capabilities. Results: Men with alexithymia demonstrated less cerebral activation in the left mediofrontal-paracingulate cortex in response to highly negative stimuli and more activation in the anterior cingulate, mediofrontal cortex, and middle frontal gyrus in response to highly positive stimuli than men without alexithymia. Conclusions: These findings provide direct evidence that alexithymia, a personality trait playing a role in affect regulation, is linked with differences in anterior cingulate and mediofrontal activity during emotional stimuli processing.