The paradox presented by the "masochist" who persists in behaviors that are followed contingently be seemingly aversive consequences is analyzed. Prototypical data from infra-human experiments are evaluated for their bearing on two theories of self-punitive actions, one based on traditional stimulus-response principles, the other on cognitive assumptions. Although the label "self-punitive" is widely used, a question remains as to whether animals that react so as to bring about so-called noxious outcomes are properly to be described as "punishing themselves." In an attempt to resolve this question, two major conceptions of punishment are evaluated as they apply to self-punitive studies. Neither conception is deemed adequate because of a lack of criteria for determining which events are aversive. A search for criteria of aversiveness eventuates in a completely relativistic view in which noxiousness and attractiveness are judged to be relational rather than absolute properties of events.