Summary:This report describes changes in sexual behavior of 209 heterosexual men enrolled in a prospective study since 1984. Data were analyzed separately for men who married during the 60 months of follow-up. Study subjects reported fewer total sexual partners and an increase in condom use in the more recent time periods compared to the first period. The proportion of never married men reporting two or more partners in the previous 6 months decreased from 53.2 to 40.7%. All of these men were human immunodeficiency virus seronegative on entry and only one documented seroconversion occurred during the follow-up.