We investigated the association between socioeconomic and behavioral factors and HIV infection and aids in a medium-sized Brazilian city. Cases included HIV-positive women (n=144) and women with aids (n=130) seen at a specialized facility. Controls were a probabilistic, population-based sample of 1,537 women aged 15-49 years. Groups were compared using logistic regression. Both HIV infection and AIDS were more frequent among younger women of non-white skin colour, with lower schooling and income who began sexual activity early. This is the first Brazilian study using population-based controls to show that both HIV-seropositivity and AIDS are concentrated among young, non-white poor women. It is important to prioritize preventive measures targeting these groups.