In this paper we present the results from a “corruption game” (a dictator game modified so that the second player can accept a side payment that reduces the overall size of the pie). Dictators (silently) treated to have the possibility of taking a larger proportion of the recipient’s tokens, take more of them. They were also more likely to report believing that the recipient would accept a low price in exchange for a side payment; and selected larger numbers as their best guess of the likely proportion of recipients acting “unfairly”. The results favor the hypothesis that people avoid altruistic actions by distorting beliefs about others.Institutional subscribers to the NBER working paper series, and residents of developing countries may download this paper without additional charge at www.nber.org.