The Southern United States (US) bears a disproportionate burden of HIV and sexually transmitted infections (STIs). HIV-infected women in this region experience higher rates of HIV-related morbidity and mortality. For HIV-infected women, STI infection may increase morbidity and facilitate HIV transmission to sex partners. Features of the social and built environment, such as high levels of poverty and low male:female sex ratios, are associated with HIV/STIs and sexual risk behaviors among HIV-uninfected populations. However, no multilevel studies have explored these relationships in a predominantly HIV-infected cohort. It is unclear how neighborhood characteristics influence sexual risk and create vulnerability to STI acquistion for people living with HIV. By integrating Women's Interagency HIV Study (WIHS) data with data from administrative sources (e.g., US Census), the proposed study will be the first to use a longitudinal, multilevel design to investigate relationships of neighborhood contexts to sexual risk behavior and STIs in a predominantly HIV-infected cohort of women living in the Southern US. The specific aims are: Aim 1. Examine cross-sectional associations between neighborhood characteristics (i.e., economic disadvantage, residential instability, male:female sex ratios, STI prevalence, social disorder) and sexual risk behaviors (i.e., HIV status of sex partner at most recent vaginal and anal sex, partner risk) among HIV-infected women screened for WIHS at the Southern Clinical Research Sites (CRSs), and investigate whether the associations between neighborhood characteristics and sexual risk behaviors that are found for HIV-positive women are similar for high-risk HIV-uninfected women. Subaim 1a. Explore the role of collective efficacy (e.g., mediator, moderator) in the relationships between social disorder and sexual risk behaviors. Aim 2. Assess the relationships between changes in neighborhood characteristics and changes in sexual risk behaviors (i.e., unprotected vaginal and anal sex, HIV status of partner at most recent vaginal and anal sex, number of sexual partners) over time among HIV-infected women enrolled in WIHS at the Southern CRSs, and investigate whether the associations between neighborhood characteristics and sexual risk behaviors that are found for HIV-positive women are similar for high-risk HIV-uninfected women. Aim 3. Assess the relationships between changes in neighborhood characteristics to changes in the probability of testing positive for trichomonas vaginalis over time among HIV-infected women enrolled in WIHS at the Southern CRSs, and investigate whether the associations between neighborhood characteristics and STIs that are found for HIV-positive women are similar are similar for high-risk HIV-uninfected women. The proposed analyses are informed by the Socioecological Framework and the Theories of Social Disorder and Collective Efficacy, and will advance our knowledge of how neighborhood-level characteristics influence sexual risk behavior and STIs over time among HIV-infected and high-risk uninfected women in the South.