Steady partners are a major source of HIV infection among gay men. To better understand sexual risk taking in steady relationships, we examined characteristics of the first incident of unprotected anal intercourse (UAI) between steady male partners. We also examined cognitive barriers to safer sex by way of associating beliefs regarding UAI with protective behavior. Questionnaires assessing sexual behavior and related cognitions were completed by 324 gay men, aged 18-34. Of the men who had UAI with their steady partners, 55% (103/189) did so within the first 3 months of the relationship, and 46% did not discuss having UAI with their partner before it occurred. Analyses revealed that perceiving UAI as a symbol of trust and believing that the partner desired UAI were associated with less condom use but also with a higher likelihood that men established HIV-negative seroconcordance and made sexual agreements (i.e., practiced negotiated safety). Perceiving UAI as more gratifying was associated with having risky UAI. Our findings suggest that interventions can make use of beliefs regarding trust and partner's desire for UAI to promote negotiated safety. In relationships where negotiated safety cannot be implemented, HIV prevention should regard the above beliefs, in particular the perception that UAI is more gratifying, as important barriers to safer sex. Furthermore, our findings regarding the early onset of risk in relationships emphasize how little time is at hand to prevent sexual risk before it occurs. One solution could be to target single gay men for promoting safer sex with future steady partners.