Sexual minority (SM) young adults, such as those who identify as lesbian, gay, or bisexual (LGB), have well documented smoking disparities compared to heterosexual young adults. However, no studies have simultaneously tested the role of three risk factors (depressive symptoms, recalling tobacco marketing in bars, and cigarette-related social norms) to explain SM tobacco use disparities. Longitudinal structural equation modeling was used to explore if the association between SM identity and past 30-day cigarette smoking one year later was mediated by these three risk factors. Starting in fall 2015, three surveys were administered every 6 months to 3,972 young adult college students. Surveys assessed SM identity, depressive symptoms, tobacco marketing in bars, normative perceptions of cigarettes, and tobacco use behaviors. Greater depressive symptoms, recalling more tobacco marketing in bars, and more accepting cigarette-related social norms were each hypothesized to explain a unique portion of the association between SM identity and subsequent cigarette use. SM young adults reported higher prevalence of cigarette use, depressive symptom scores reflecting elevated risk for major depressive disorder, and more accepting cigarette-related social norms than their heterosexual peers. Results indicated that only cigarette-related social norms mediated the association between SM identity and subsequent past 30-day smoking, while controlling for depressive symptoms, recalling tobacco marketing in bars, sociodemographic factors, and previous tobacco use. Findings reflect a need for tailored tobacco control messaging that shift the more accepting cigarette-related norms of SM young adults, as doing so may ultimately lead to decreased smoking for this high-risk subgroup. (PsycINFO Database Record (c) 2019 APA, all rights reserved).