BACKGROUND:Sexual minority young adults have higher smoking rates than the general young adult population, but reasons for this disparity are poorly understood. The current study aimed to: 1) identify real-time predictors of smoking among sexual minority and heterosexual smokers and 2) examine between-group differences in these predictors. METHODS:We conducted an ecological momentary assessment (EMA) study in the San Francisco Bay Area, California in 2016-2017. Data from 84 young adult smokers (44% identified as sexual minority, including 29 bisexual and 8 gay/lesbian) with 6498 EMA assessments were analyzed. Both internal and external predictors and interaction terms between each predictor and sexual group were examined using generalized estimating equation models. RESULTS:Common correlates of smoking were found for both groups (e.g., craving, absence of smoking bans, presence of other smokers, outside location, and seeing triggers). Unique factors for sexual minority smokers were being at a bar (aOR = 1.75, 95% CI = 1.06-2.90) and the number of other smokers present (aOR = 1.12, 95%CI = 1.04-1.20), while the presence of a smoking family member reduced the odds of smoking in this group (aOR = 0.13, 95%CI = 0.02-0.85). In interaction models, the number of other smokers exerted a greater influence on sexual minority participants compared to their heterosexual counterparts (aOR = 1.10, 95%CI = 1.01-1.20), while craving (aOR = 0.84, 95%CI = 0.75-0.93) and presence of a smoking family member (aOR = 0.11, 95%CI = 0.01-0.82) had weaker influences. CONCLUSIONS:Our study highlights unique situational factors associated with smoking among sexual minority young adults and differences in these factors by sexual identity. Future interventions targeting sexual minorities should address bar attendance and specific triggers.