Discussions about the cultural dimensions of the spread of HIV/AIDS in Africa persist. Drawing on data on fish-for-sex deals between local Ila or Tonga women and immigrant fishermen in the Zambian Kafue Flats, we argue against the notion that traditional institutions governing extra-marital sexual relationships are responsible for the spread of HIV/AIDS. We argue that fish-for-sex exchanges are based not on tradition, but on the economic opportunities provided by the fish trade in conditions of poverty and changing livelihoods. Stigmatization of women involved in fish-for-sex deals is, however, on the increase, since they are accused of spreading the disease in their community. Women's inability to follow the sexual prescriptions conveyed by HIV prevention programmes produces shame and moral distress, associated with the fear of social exclusion. In this situation, lubambo, a former customary regulation of extramarital sexual relations among the Ila, may provide women with legitimacy for sexual transactions. Additionally, customary marriage arrangements institutionally secure their access to fish.