There are stable between-person differences in an internalizing "trait," or the propensity to experience symptoms of internalizing disorders, such as social anxiety, generalized anxiety disorder, and depression. Trait internalizing may serve as a marker of heightened risk for problem alcohol outcomes (such as heavier drinking, binge drinking, or alcohol dependence). However, prior research on the association between internalizing symptoms and alcohol outcomes has been largely mixed in adolescence, with more consistent support for an association during adulthood. It may be that trait internalizing is only associated with problem alcohol outcomes in adulthood, after individuals have gained experience with alcohol. Some evidence suggested that these effects may be stronger for women than men. We used data from a community sample (n = 790) interviewed during adolescence (ages 14-16) and again at ages 21, 24, 27, 30, 33, and 39. Using generalized estimating equations, we tested the association between trait internalizing and alcohol outcomes during both adolescence and adulthood, and tested whether adult trait internalizing mediated the association between adolescent trait internalizing and adult alcohol outcomes. Trait internalizing in adulthood (but not adolescence) was associated with more frequent alcohol use, binge drinking and symptoms of alcohol use disorders, and mediated the effects of adolescent trait internalizing on alcohol outcomes. We observed no moderation by gender or change in these associations over time. Understanding the developmental pathways of trait internalizing may provide further insights into preventing the emergence of problem alcohol use behavior during adulthood. (PsycInfo Database Record (c) 2020 APA, all rights reserved).