This paper explores how men who have sex with men (MSM) with diagnosed HIV who engage in unprotected anal intercourse (UAI) perceive the potential risk of superinfection and how they respond to it. Semistructured interviews were carried out with 42 MSM recruited via community-based agencies throughout England and Wales. The interviews examined sexual risk taking and the ways in which men sought to manage the risks they perceived. All participants had heard of superinfection and one-third considered it a personal risk when they had UAI with men with the same sero-status. The risk of being superinfected with HIV was often situated among a number of other concerns that men felt they needed to manage when having sex. There was significant uncertainty about the likelihood of acquiring an additional strain of HIV, which was exacerbated by competing, and often conflicting, advice from a variety of expert sources. Men frequently drew upon lay and expert understandings of viral load and infectiousness to rationalize engagement in UAI with other diagnosed positive men. HIV health-care providers should seek to find consensus on how to discuss superinfection with MSM, taking account of the array of other physical and social risks associated with sex.