More HIV prevention research is needed to better understand how relationship factors may affect sexual risk behaviors among gay male couples. Our cross-sectional study collected dyadic data from 144 gay male couples to examine which relationship factors and characteristics were associated with men having UAI with a secondary sex partner. We targeted male couples by using a variety of recruitment strategies. Multilevel random-effects logistic regression modeling was used to examine which factors were predictive of men in gay couples who had UAI with a secondary sex partner. Analyses revealed that men were less likely to have had UAI with a secondary sex partner if they reported being in a strictly monogamous relationship, receiving an HIV test within the previous 3 months, and being committed to their sexual agreement. Future HIV prevention interventions must consider how relationship factors may influence sexual risk behaviors among gay male couples.