Research shows that young men who have sex with men (YMSM) engage in higher rates of health risk behaviors and experience higher rates of negative health outcomes than their peers. The purpose of this study is to determine if the effects of adversity on HIV risk are mediated by syndemics (co-occurring health problems). Participants were 470 ethnically diverse YMSM ages 18 to 24 recruited between 2005 and 2006 and surveyed every 6 months for 24 months. Regression analyses examined the impact of adversity on syndemics (emotional distress, substance use, and problematic alcohol use) and the effects of both adversity and syndemics on HIV risk behaviors over time. Gay-related discrimination and victimization-among other adversity variables-were significantly associated with syndemics and condomless sex (CS). Syndemics mediated the effects of adversity on CS in all models. Adverse events impact HIV risk taking among YMSM through syndemics. These findings suggest that prevention programs aimed at reducing adversity may reduce both the synergistic effect of multiple psychosocial health problems and HIV risk taking.