This report describes the sexual behavior with "extramarital" partners of men who are in committed relationships with men of opposite HIV status. We examined the rates of unprotected anal sex with outside partners and compared these rates with the prevalence of such activity within the couple, during the year prior to the assessment. Seventy-five couples were interviewed, of whom 50 (67%) reported sex outside of the primary relationship by one or both members of the couple. Rates of unprotected anal sex with one-night stands and "other" partners were 25% and 33%, respectively among men who engaged in anal sex with such partners. In contrast, 54% of the men who engaged in anal sex with their primary partner did not always use condoms. Data from men who engaged in anal sex with both their primary partner and one-night stand(s) revealed that condoms were used less frequently within the primary relationship when the HIV negative men were the insertive partner; otherwise the rates of unprotected anal sex were similar. Approximately 75% of HIV negative men who engaged in receptive anal sex always used condoms, and a similar proportion of HIV positive men always used condoms during insertive anal sex, regardless of partner type. The vast majority of unprotected anal sex occurred without ejaculation inside the rectum. Unprotected oral sex was highly prevalent regardless of partner type. Implications for public health policy and primary prevention research are discussed.