This paper reports on the perceptions and practices of men who have frequent unprotected sex with men in a socio-legal environment defined by the 1998 decision of the Supreme Court of Canada in R. v. Cuerrier. HIV-positive people are increasingly finding themselves in court since Cuerrier, and many are trying to take account of legal reasoning in their own conduct. The judicial construction of behaviour likely to transmit HIV relies on a set of presumptions concerning individual responsibility, rational and contractual interaction, and consenting adults that raises a series of ambiguities and uncertainties among HIV-positive people attempting to implement them in everyday life. While some express support for the reasoning in Cuerrier, others struggle with practical dilemmas in sexual interaction, and a minority strand of ethical reasoning advances a “buyer beware” principle. This latter view occurs in a social environment where HIV-positive people experience strong disincentives to disclose in the face of potential rejection or discrimination once their sero-status is known. Examination of the social consequences of Cuerrier raises questions about the viability of relying on the enforcement of disclosure, through threat of criminal prosecution, as an effective method of HIV prevention, especially when most practical, day-to-day HIV prevention occurs when safer sex is practised consistently regardless of disclosure.