Research has demonstrated that children’s pain is underestimated in clinical settings. Nurses in particular have been highlighted as the professional group most likely to underestimate their pain. Contemporary theories of evolutionary psychology propose that pain assessment is a social exchange situation (e.g. Kappeser et al. 2006), whereby benefits (analgesia) are exchanged with another person when they have paid a cost (pain). A social contract is the cognitive mechanism that supports the exchange of benefits between people. It was proposed in this study, that nurses enter into a social contract with their patient in a pain assessment scenario. Additionally it was suggested that the underestimation of pain occurs in response to cheater-detection; a cognitive mechanism that has developed to ensure the fair distribution of benefits to people in need. It was hypothesised that when rating in a social contract condition, nursing students would impute less pain than when they were rating in a non-social contract condition. This effect would be strengthend when the participant suspected cheating. It was also proposed that participants in the social contract condition would rate higher levels of exaggeration and would be less likely to reduce pain when they suspected cheating.