Although the prefrontal cortex (PFC) has been implicated in aspects of behaviour relating to honesty, the mechanisms and circuits involved are unknown. The authors tested the responses of people in games in which subjects had to decide between self-interest and honesty. People with lesions to the dorsolateral region of the PFC (DLPFC) had fewer concerns about the honesty of a particular decision than healthy participants. These data suggest that the role of the DLPFC could be to rein in self-interest urges, allowing more honest decisions to be made.