Adverse childhood experiences (ACEs) predict problematic health outcomes (eg, substance use, mental health) among young adults; whether specific ACEs are differentially associated with specific substance use and mental health symptoms is understudied. Latent class analysis (LCA) identified classes of ACEs among 2209 US young adults (Mage = 24.69, range: 18-34; 57.4% female; 30.9% sexual minority; 35.8% racial/ethnic minority) in a 2-year study (2018-2020). Multivariable logistic regressions examined ACEs (reported in 2019) in relation to 2020 reports of current (past 30-day) substance use (ie, tobacco use; cannabis use and hazardous use; alcohol use and binge drinking) and mental health (ie, ≥moderate depression and anxiety symptoms), controlling for sociodemographics (ie, age, gender, race, ethnicity, sexual orientation, education). Overall, 65.4% reported ≥1 ACE (M = 2.09, SD = 2.30); 34.8%, 39.1%, and 71.1% current tobacco, cannabis, and alcohol use; 39.1% and 15.3% hazardous cannabis use and binge drinking; and 24.2% and 34.5% ≥moderate depression and anxiety symptoms, respectively. LCA yielded 4 classes: Low ACEs (referent; 55.6%), Poor family health and divorce (16.3%), Parental abuse (16.0%), and High ACEs (12.1%). High ACEs (vs Low ACEs) was associated with each adverse substance use and mental health outcome except alcohol use. Poor family health and divorce was associated with tobacco use, cannabis use, and both mental health outcomes. Parental abuse was associated with tobacco use, cannabis use, hazardous cannabis use, and both mental health outcomes. Health promotion interventions for young adults must assess ACEs, given that certain types of ACEs may be associated with distinct substance use and mental health outcomes.