Adverse childhood experiences (ACEs) are preventable, potentially traumatic events with lifelong negative impacts. Population-level data on ACEs among adolescents have historically relied on parent reports and excluded abuse-related ACEs. We present the self-reported prevalence of ACEs among a large population-based sample of US high school students. Using cross-sectional, state-representative data from 16 states that included core ACE questions on their 2021 Youth Risk Behavior Survey, we estimate the prevalence of 8 individual (lifetime emotional, physical, or sexual abuse, physical neglect, witnessed intimate partner violence, household substance use, household poor mental health, incarcerated parent or guardian) and cumulative ACEs (0, 1, 2-3, ≥4) among a large population-based sample of adolescents, overall and by demographic characteristics (sex, race and ethnicity, age, sexual orientation). Emotional abuse (65.8%), household poor mental health (36.1%), and physical abuse (32.5%) had the highest prevalence. ACEs were very common, with 80.5% of adolescents experiencing at least 1 ACE and 22.4% experiencing ≥4 ACEs. Experiencing ≥4 ACEs was highest among adolescents who were female (27.7%), non-Hispanic multiracial (33.7%), non-Hispanic American Indian or Alaska Native (27.1%), gay or lesbian (36.5%), bisexual (42.1%), or who described their sexual identity some other way or were not sure of their sexual identity (questioning) (36.5%). Self-reported ACE estimates among adolescents exceed previously published parent-reported estimates. ACEs are not equally distributed, with important differences in individual and cumulative ACEs by demographic characteristics. Collecting ACE data directly from adolescents at the state level provides actionable data for prevention and mitigation.