Previous studies investigating altruistic punishment have confounded the effects of two independent variables: information transmission (or breach of privacy) and personal identification (or breach of anonymity). Here we report findings from a brief study in which participants were asked to respond to a social norm violation (i.e., an anonymous actor had behaved selfishly in an economic game) by deciding whether to sacrifice their own endowment to punish this person. A third of the participants were told that their economic decisions would be made known to another player but could not be identified (privacy breach condition), whereas another third were informed that their decision as well as their names would be made known (anonymity breach condition). (The decisions of control participants were completely anonymous and private.) Participants also justified their economic decisions and reported their emotional experiences. The results were participants punished most in the privacy and anonymity breach conditions and least in the control condition. These findings have implications for existing evolutionary accounts of altruistic punishment.