--- - |2 Abstract Relationship characteristics, levels of anticipated sexual jealousy, and correlates of anticipated sexual jealousy were compared for heterosexual and homosexual men sampled from 1980 and 1992. Homosexual and heterosexual relationships were similar on relationship involvement, but homosexual (vs. heterosexual) respondents indicated lower levels of experiencing and expressing sexual jealousy, less exclusive relationships, higher levels of extradyadic sexual relations by their partners, larger number of relationships, and relationships of shorter duration. Cohort comparisons indicated that both groups of men in 1992 (vs. 1980) had higher levels of experiencing and expressing jealousy caused by the partner's extradyadic sexual behavior, more exclusive romantic relationships, fewer relationships, and relationships of longer duration. These changes suggest a transition in men's relationships that may be related to the increase in sexually transmitted diseases in general and AIDS in particular. - Personal Relationships, Page 313-325, October 2018.