Background: Discrimination and stigmatization at the institutional and sociocultural level (conceptualized as "structural stigma") has been associated with adverse health outcomes among sexual and gender minorities. However, few studies explore whether structural stigma is associated with sexual health outcomes. Addressing this gap, here, we explore this relationship among Australian gay, bisexual, and other men who have sex with men (GBM)-a population disproportionately affected by HIV.Setting and Methods: Using responses from the 2017 Australian Marriage Law Postal Survey, we operationalized structural stigma related to sexual minority status as the regional percentage of votes against legalizing same-sex marriage. These responses were then linked to national HIV behavioral surveillance data from Australian GBM (43,811 responses between 2015 and. Controlling for a rich set of individual and regional level confounders, regression analyses were used to estimate the extent to which structural stigma was associated with testing for, and diagnoses of, HIV and sexually transmitted infections (STIs), and awareness and use of HIV prevention and treatment interventions (pre-exposure and postexposure prophylaxis, combination therapy, and HIV-related clinical care).Results: Australian GBM living in regions with higher levels of structural stigma were less likely to undergo HIV/STI testing, receive HIV/STI diagnoses, and be taking, or aware of, biomedical prevention strategies. Among GBM living with HIV, structural stigma was associated with a reduced likelihood of being on combination therapy and fewer HIV-related clinical visits.Conclusions: Altogether, these results suggest that structural stigma may undermine HIV prevention strategies as well as adequate management of HIV infection among GBM.