Among youth from high-achieving schools, adverse childhood experiences (ACEs) were examined in relation to (a) internalizing and externalizing symptoms in adolescence (n = 527), and (b) symptoms plus psychiatric diagnoses-based on multiple annual interviews-in adulthood (n = 316). Also examined were associations for a "Proxy ACEs" (P-ACEs) measure, containing items similar to those on standard ACEs measures without reference to abuse or neglect. Rates of ACEs were comparable with those in other studies; most commonly endorsed were perceived parental depression followed by aspects of emotional neglect. Groups exposed to zero, 1, 2, 3, and 4+ ACEs differed on symptoms in adulthood, with small to moderate effect sizes; in parallel comparisons of P-ACEs groups on Grade 12 symptoms, differences had large effect sizes. In relation to psychiatric diagnoses, comparisons with the zero ACEs group showed that groups with 1, 2, 3 ACEs, versus 4+ ACES, respectively, had twofold and over fivefold greater odds of having any lifetime diagnosis. The odds for internalizing diagnoses specifically were 2-6 times greater for individuals with 1, 2, and 3 ACEs, and 12 times greater for those reporting 4 ACEs. Remarkably, Grade 12 reports of 2, 3, and 4+ P-ACEs were linked to 2-3 times greater odds of a psychiatric disorder in adulthood, and 3-6 times greater odds for internalizing diagnoses specifically. In the future, assessments of ACEs and P-ACEs could facilitate early detection of problems among HAS students, informing interventions to mitigate vulnerability processes and promote resilience among these youth and their families. (PsycInfo Database Record (c) 2021 APA, all rights reserved).