This paper focuses on cross-cultural differences in sexual jealousy. It is assumed that cultures differ (a) in the incidence of sexual jealousy, (b) in the range of acceptable strategies for coping with a jealousy situations and (c) in the behavior evoking sexual jealousy.. We addressed the last aspect. Subjects were 2,079 students from seven industrialized nations: Hungary, Ireland, Mexico, the Netherlands, the Soviet Union, the United States, and Yugoslavia Results showed that in nearly all of these nations, kissing, flirting, and sexual involvement of one of the partners with an interloper evoked jealousy. On the other hand, dancing, hugging, and sexual fantasies led, on the average, to a neutral reaction in all nations surveyed. Nevertheless, there were striking cross-national differences in the relative value attached to a particular behavior. Furthermore, there were cross-cultural sex, differences. In all seven nations, women became more upset when their partner kissed someone else, and men reacted relatively more negatively to sexual fantasies of their partners about another person. The data are discussed in relation to the question of to what degree human sexual behavior is genetically or culturally determined.