Objective: The current study examined effects of the presence of a misogynistic male peer norm and masculine gender role stress (MGRS) on bystander intervention behavior for sexual aggression. Method: Undergraduate men (N = 104) engaged in a novel laboratory paradigm in which they and 3 male confederates watched a female confederate, who reported a strong dislike of sexual content in the media, view a sexually explicit film which they could stop at any time. Prior to the female viewing the film, participants were randomly assigned to an audience manipulation wherein the male confederates set a misogynistic or ambiguous group norm. Results: Zero-inflated negative binomial (ZINB) regression models indicated (a) the presence of a misogynistic peer norm decreased the odds of intervening, and (b) higher levels of MGRS significantly increased the rate of bystander intervention among participants exposed to a misogynistic, but not an ambiguous, norm. Conclusions: Findings highlight the importance of examining situational and individual level factors that may influence prosocial bystander intervention behavior to prevent sexual aggression. (PsycINFO Database Record (c) 2017 APA, all rights reserved)