Safer sex in the context of HIV/AIDS control in Kenya has mainly been promoted through the encouragement of condom use. In this strategy, safer sex is treated as though it is synonymous with condom use. This paper, which is based on ethnographic data drawn from a sample of 29 heterosexual HIV-positive patients presenting in four specialized treatment clinics in Nairobi, questions this assumption by examining some particular ways in which risks of HIV/AIDS are socially constructed, and how these perceptions have informed lay experiences of safer sex in Nairobi. The paper further examines the juxtaposition of common-sense and biomedical knowledge in producing socially meaningful experiences of safer sex. The implications of these lay safer sex constructions and experiences for government-sponsored HIV/AIDS control programmes and policies are discussed.