The goal of this study was to determine whether, at different age levels, males cite different bases as reasons for disliking peers. Male preschoolers, primary graders, preadolescents, and young adults were asked to name and give reasons for disliking an actual same-sex peer. Participants from preschool through preadolescence frequently cited aggression and aberrant behavior as reasons for disliking, a finding that suggests that both dimensions serve as major sources of enmity across childhood. Although aggression was not cited frequently by the young adults, aberrant behavior persisted as a significant basis for disliking across all four developmental levels. Lack of general play and rule violation constituted reliable bases for disliking only at the preschool level, whereas lack of help was cited frequently by both the primary-grade and preadolescent participants. The preadolescents and the young adults also specified negative evaluation as a major basis of enmity, whereas lack of genuineness was cited at above-chance levels only by the young adults.