Men who have sex with men (MSM) are disproportionally affected by HIV. Although some theoretical models created to explain why individuals engage in risky sexual behavior contain an affective component, there has been relatively little focus on the influence of affect on sexual risk-taking. The goal of this study is to investigate the association between affect and condom use among MSM using an archival dataset from a survey of users of a popular sex-oriented website. Multilevel modeling was used to analyze daily diary data from 2871 MSM. At the within-person level, positive affect was positively related to condomless anal sex (CAS), whereas negative affect was negatively related to CAS. However, these results were qualified by interactions of trait affect and relationship to sex partner. These findings suggest that interventions focused on emotional regulation may have the potential to reduce CAS among MSM.