Unprotected anal intercourse among men-who-have-sex-with-men (MSM) occurs more frequently between partners in a primary relationship than between nonprimary partners. Although research supports the role of social support in risky sex, findings also suggest that the reasons associated with risky sex differ depending on both the relationship status and HIV-serostatus of MSM. This study assessed whether level of intimacy within a primary relationship helps to explain risky sex among a sample of 78 HIV-positive MSM currently involved in a primary relationship. Findings suggest that both drug use prior to sex and HIV status of the primary partner moderate the relationship between intimacy and sexual risk behaviors. Under levels of low drug use, greater intimacy functioned as a protective factor within seroconcordant relationships whereas it functioned as a risk factor within serodiscordant relationships. Implications for educational and clinical interventions are discussed.