Male norms about aggression may be perpetuated in part by the belief that aggression is more expected or socially desirable than it really is. This paper explores the accuracy of people’s beliefs about the acceptability of aggression by examining men’s perceptions of descriptive (what their peers do) and injunctive norms (what their peers approve of or desire). Study 1 found that men (but not women) overestimated the aggressiveness of their peers. Study 2 demonstrated that men (but not women) overestimated peer approval of aggression and disapproval when an affront was not responded to aggressively. Study 3 found that men overestimate how attractive aggression is to women. Study 4 found that greater perceived discrepancies in aggression between self and peers was related to lower self-esteem, a weaker gender identification, and greater feelings of social marginalization, suggesting that men’s misperceptions about aggression norms have negative consequences for self-perceptions