The overarching goal of this proposed study is to leverage existing and ongoing data to examine the role of sexual behavior stigma on access to HIV healthcare as well as sexual and mental health outcomes among men who have sex with men (MSM). Worldwide MSM are a key population that bear a disproportionate burden of HIV with high prevalence and incidence yet they have low uptake and/or access to treatment and prevention. Consistent with NIH HIV/AIDS research priorities, the proposed project aims to reduce health disparities in HIV infection and treatment outcomes by addressing stigma towards MSM in the context of intersecting stigmas and potentially modifiable mediators (e.g., depression). In particular, validated measures of sexual behavior stigma are needed to effectively measure stigma-related interventions and to better understand the mechanisms of how stigma potentiates HIV risks among this key population. We propose to leverage existing data collected from over 15,000 MSM across 7 different Sub-Saharan African nations, the American Men's Internet Survey (AMIS), the UCLA mSTUDY, and the HIV Prevention Trials Network (HPTN) 078 study on Enhancing Recruitment, Linkage to Care and Treatment for HIV-Infected MSM in the US. The specific aims of the work are: Aim 1) Develop validated measures used to assess sexual behavior stigma among MSM using factor analysis and validity and reliability testing. This will result in finalized stigma metrics and recommendations for integration of MSM stigma items that can be used in future studies. Aim 2) Identify specific mediated associations between stigma and HIV-related outcomes using structural equation modeling. In addition, test for intersectionality of multiple forms of stigma (e.g., gender, HIV status, race/ethnicity) using an inter- and intra-categorical approach. The delivered outcomes will include quantified associations of sexual behavior stigma with HIV-related outcomes that can be used to inform HIV intervention planning by setting feasible targets for stigma mitigation interventions. Aim 3) Include final validated stigma metrics in an upcoming cycle of AMIS and bio-validate the stigma metrics. Bio-validation will consist of testing associations of sexual behavior stigma with testing positive for sexually transmitted infections (chlamydia and gonorrhea), and with chronic stress measured using telomere DNA length. Participants will self-collect urine, rectal, and saliva specimens using home-based STI test kits. Overall, the proposed study will result in a thorough assessment of a sexual behavior stigma scale for MSM and how it operates comparatively with other types of stigma. The validated stigma metrics will provide recommendations for future studies that seek to measure stigma and its relation to HIV among this key population.