Since the 1980s, no significant negative relationship exists in sub-Saharan Africa between adult mortality and urbanization. In the rest of the world, the relationship between adult mortality and urbanization is significantly negative. High prevalence of HIV likely explains the absence of a significant negative relationship between adult mortality and urbanization in sub-Saharan Africa. HIV can spread more rapidly in the city than in the countryside because the costs of finding multiple sexual partners are lower in the city than in the countryside. During the 1960s and 1970s, i.e. prior to the HIV pandemic, adult mortality and urbanization are significantly negatively correlated in sub-Saharan Africa.