How we are viewed by other individuals-our reputation-has a considerable influence on our everyday behaviors and is considered an important concept in explaining altruism, a uniquely human trait. Previously it has been proposed that processing one's own reputation requires a reputation representation in the medial prefrontal cortex (mPFC) and a value representation in the striatum. Here, we directly tested this idea using functional magnetic resonance imaging (fMRI). Subjects disclosed their behavioral tendencies with reference to social norms in the presence or absence of other people, a manipulation that is known to greatly affect an individual's concern for their reputation. The mPFC showed strong activation during self-referential processing, and this activity was enhanced by the mere presence of observers. Moreover, the striatum was also strongly activated when subjects responded in front of observers. Thus, the present study demonstrated that the mPFC and striatum were automatically recruited when the task placed a high demand on processing how one is viewed by others. Taken together, our findings suggest that the mPFC and the striatum play a key role in regulating human social behaviors, and these results provide valuable insight into the neural basis of human altruism.