The HIV/AIDS epidemic in South Africa is more severe than almost anywhere else in the world and continues to grow. Here, and elsewhere in southern Africa, it is now a generalized epidemic, largely heterosexually spread. This is very different from the more limited epidemic in the United States of America and other developed countries. It was in the USA in the five years after the first cases of AIDS that the understandings and explanations of HIV/AIDS were constructed. HIVIAIDS was defined as a transmittable infection causing a progressive deterioration of the immune system, leaving it vulnerable to opportunistic infections and disease of increasing severity resulting in inevitable death. Virology identified the virus that is the infectious agent and provided explanations of how it had its effect on the host, reproduced and was transmitted. Influenced by the early association of AIDS with homosexuals, the social construction of HIVIAIDS has focused on risk groups and risk behaviours. These are now central components of a dominant paradigm that has informed but also limited research. This paradigm also informs and limits responses to and strategies to prevent the spread of the virus.