OBJECTIVES:A range of HIV risk reduction strategies has been described in homosexual men who practice unprotected anal intercourse (UAI), including serosorting, strategic positioning, and negotiating around an HIV-positive partner's viral load. It is uncertain how commonly these behaviors might result in HIV infection. We describe sexual behaviors and associated risk reduction strategies reported by homosexual men in their accounts of their recent seroconversion. METHODS:Homosexual men recently diagnosed with primary HIV infection between 2003 and 2006 were invited to participate in a nurse-administered survey. RESULTS:Among 158 men enrolled, 143 (91%) were able to identify the high-risk event that they believed led to their HIV seroconversion, and this involved UAI in 102 (71%). Among these 102 men, 21 (21%) reported they were certain that the source partner was HIV-negative. Ten men (10%) reported insertive UAI as the highest risk behavior. Of the 21 men who reported knowing the HIV-positive partner's viral load, 9 reported that the man had an undetectable viral load (43%). CONCLUSION:In 38% of the high-risk events involving UAI, infection occurred when the reported risk event involved serosorting, strategic positioning, or intercourse with a man whose viral load was believed to be undetectable.