In the context of sexual prejudice, in which group distinctiveness motivation is particularly strong for men, three studies tested the hypothesis that egalitarian norms can intensify reactive distinctiveness motives, and then paradoxically increase intergroup differentiation and prejudice. Depending on the studies, the egalitarian norm was experimentally manipulated or induced and kept constant. Group distinctiveness was manipulated through scientific support for the theory that a person’s sexual orientation is determined by biological factors in terms of the extant biological differences (high distinctiveness) versus biological similarities (low distinctiveness) between heterosexual and gay people. Egalitarian norms increased men’s (but not women’s) intergroup differentiation (Study 1) and prejudice (Study 2) when group distinctiveness was low (as compared to high). This pattern was specific to men with high gender self-esteem, and appeared when the biological theory was framed in terms of intergroup differences rather than the uncontrollability of sexual orientation (Study 3).