MTN-009 is a multi-site, cross-sectional study that will provide an estimate of the prevalence of ARV resistance in the population of women who present to study sites to be pre-screened or screened for participation in an HIV prevention trial. To date, a comprehensive surveillance of HIV drug resistance in newly diagnosed women of reproductive age has yet to be undertaken. The primary goal of MTN-009 is to assess the frequency of HIV drug resistance mutations among women who test HIV-positive when presenting to screen for participation in HIV prevention trials. Secondary aims include the identification and evaluation of behavioral indicators including self or sexual partner(s) exposures to antiretroviral (ARV) drugs as risk factors for drug resistant HIV infection, as well as the characterization of the degree of immunodeficiency and risk of disease progression by quantifying plasma HIV-1 RNA and CD4-positive T cells among women who test HIV-positive when presenting to screen for participation in an HIV prevention trial. Exploratory aims include the identification of polymorphic or subtype-specific sequence changes in HIV-1 that may impact susceptibility to ARVs, and the estimation of the proportion of HIV-positive women who have chronic versus recent HIV infection.