Persistent preexposure prophylaxis (PrEP) use reduces the risk of HIV infection, yet uptake lags among those with the greatest need. Sexual identity stigma may be a significant barrier to PrEP awareness and use among high-risk communities. The primary aim of this study was to determine whether sexual identity was related to PrEP awareness and use. This multisite HIV Prevention Trials Network (HPTN) study (HPTN 078) focuses on men who have sex with men (MSM; n = 335) who were HIV-negative at screening. The majority of participants were non-White (62.1%), younger than 35 (57.9%), single (79.1%), and aware of PrEP yet had never taken PrEP (52.5%). Participants completed questionnaires including sexual history and identity; lesbian, gay, bisexual, transgender, and queer community engagement; PrEP awareness and use; and several measures of sexual identity stigma including family and friend stigma, general societal stigma, and anticipated health care stigma. Univariate and multinomial logistic regression models helped to determine factors associated with PrEP awareness and use. There were stark disparities in PrEP awareness comparing Black and White participants; 50% of Black participants reported being PrEP unaware versus 11.8% of White participants. In this sample, gay sexual identity (compared to bisexual identity) was associated with increased PrEP awareness (aOR 6.66) and use (aOR 16.9). Additionally, 29% of the association between sexual orientation and PrEP use was mediated through internalized stigma. Given low PrEP uptake among MSM, interventions that address sexual identity stigma may motivate greater PrEP uptake. (PsycInfo Database Record (c) 2022 APA, all rights reserved)