Psychopaths show a profound lack of morality and behavioral controls in the presence of intact general intellectual functioning. Two hallmarks of psychopathy are the persistent violation of social contracts (i.e., cheating) and chronic, impulsive risky behavior. These behaviors present a puzzle: Can psychopaths understand and reason about what counts as cheating or risky behavior in a particular situation? We tested incarcerated psychopaths' and incarcerated nonpsychopaths' reasoning about social contract rules, precautionary rules, and descriptive rules using the Wason selection task. Results were consistent with our hypotheses: Psychopaths (compared with matched nonpsychopaths) showed significant impairment on social contract rules and precautionary rules, but not on descriptive rules. These results cannot be accounted for by differences in intelligence, motivation, or general antisocial tendency. These findings suggest that examination of evolutionarily identified reasoning processes can be a fruitful research approach for identifying which specific mechanisms are impaired in psychopathy.