ABSTRACT African-Americans have the highest rates of human immunodeficiency virus (HIV) transmission, including heterosexual transmission, in the United States. Although numerous factors probably contribute to the extreme racial disparity, reasons for its persistence remain poorly explained. Mathematical modeling demonstrates that concurrent sexual partnerships speed transmission of HIV through sexual networks more effectively than does serial monogamy, for the same total number of sexual partners. This paper examines the evidence that the social and economic environment for many African-Americans discourages long-term monogamy and promotes concurrent sexual partnerships, which may, in turn, fuel the HIV epidemic in this population.