Three hundred fifty-eight undergraduates completed anonymous questionnaires regarding jealousy over a mate's infidelity. More men than women predicted that sexual infidelity would be worse than emotional infidelity when given the forced-choice hypothetical measures used in previous work. When some of the implications of hypothetical infidelity were controlled, the gender difference disappeared. One hundred twenty-seven participants reported having actual experience with a mate's infidelity. The two genders did not differ in degree of focus on the sexual versus emotional aspects of a mate's real betrayal. Sexual jealousy was correlated with having a greater number of sexual relationships and, for men but not women, with placing higher importance on sex in dating relationships. The results are discussed from a social-cognitive perspective. (Contains 2 tables.)