PROJECT SUMMARY/ABSTRACT The disproportionate impact of the HIV/AIDS epidemic among U.S. Black gay, bisexual, and other men who have sex with men (GBMSM) is staggering, especially among young Black GBMSM who live in the South. Black GBMSM between ages 13 to 34 and those who live in the South accounted for 75% and 63% of HIV diagnoses among Black GBMSM in 2016, respectively. Most conceptualizations of intersectional stigma have been almost exclusively individualistic. Consequently, substantial gaps exist about how multilevel intersectional stigma — individual (e.g., internalized HIV stigma, interpersonal discrimination), community (e.g., anti-gay stigma at church) and social-structural (e.g., criminal HIV exposure laws) — interconnects to hinder HIV testing and PrEP use for young Black GBMSM in the South. There is also a dearth of validated measures of multilevel intersectional stigma for HIV prevention research. To address these critical empirical gaps, a longitudinal exploratory-sequential mixed methods study (QUAL QUANT) is proposed to refine and validate the Multilevel Intersectional Stigma Measure developed during Phase I of the parent study for young Black GBMSM in two high HIV incidence southern cities: Washington, DC and Jackson, MS. Purposive sampling will be used to recruit 150 HIV-negative young Black GBMSM, ages 15 to 34. Phase I, completed during the original funding period of the parent study, involved: (1) literature and policy reviews to identify existing measures of intersectional stigma and stigma-related laws and policies; (2) 60 in-depth individual interviews (30/city) to gain a rich and contextually-grounded understanding of multilevel intersectional stigma; and (3) content validity assessments of the self-report measures by expert judges (n = 5 to 7) and Community Advisory Board (CAB) members (n = 24; 2 CABs/city). Phase II and III in the proposed supplement remain unchanged from the parent study. Phase II involves: (1) cognitive interviews with 20 participants (10/city) to refine the self-report measures; and (2) baseline and 3-month follow-up surveys of 130 participants (65/city) for psychometric analyses. Phase III involves the synthesis of the qualitative and quantitative results and validity assessments of the synthesized results with CAB members in each city. The significance of the parent study lies in the development of new Multilevel Intersectional Stigma measures and the proposed supplement will facilitate the completion of the psychometric assessment and validation of the measures as planned despite the project experiencing COVID-19 related delays. The study makes an innovative multilevel paradigmatic shift from the status quo with its theoretical and methodological fidelity to intersectionality’s core tenets. The expected outcome is the development of new self-report and objective/non-self-report measures of multilevel intersectional stigma that reflect the “specific and particular” experiences of young Black GB...