The authors argue that, based on a biosocial model proposed by Wood and Eagly (2002), sex differences in reactions to sexual versus emotional infidelity should be mediated via gender-role related traits, whereas based on the assumption of jealousy as a specific innate module (JSIM; Buss et al. 1992), such mediation would not be predicted. In a survey study, 646 British adults reported whether sexual or emotional infidelity of an intimate partner would distress them more, and completed masculinity (M) and femininity (F) scales. Replicating previous work, females reported greater distress than males at emotional (vs. sexual) infidelity. Importantly, this sex difference was partially mediated by both M and F, which supports the biosocial model. However, biological sex remained a significant predictor even after M and F had been controlled for, suggesting that JSIM may explain part of the variance in the observed sex difference.