A wealth of research has established that adopted youth are at greater risk for impaired mental health than their non-adopted peers, given the host of early life stressors that many experience. However, the specific trajectories of risk and resilience into adulthood remain unclear. The present study examines longitudinal trajectories of mental health in 49 adolescents and young adults adopted from foster care, using data collected at six time points in childhood to predict later youth outcomes from parent-report and child-report surveys. The study investigated the contribution of two major pre-adoptive risk factors, abuse/neglect and age of adoptive placement, to childhood trajectories of behavior problems, measured by the Child Behavior Checklist (CBCL). It also utilized these risk factors and behavioral trajectories to predict current outcomes of mental health, such as psychopathological symptoms, psychiatric diagnoses, and substance abuse. Pre-adoptive abuse/neglect predicted current levels of psychopathological symptoms and diagnosis of depression, while older age of placement predicted greater alcohol use. Children adopted after age 4 initially had marginally higher CBCL externalizing scores than children adopted after age 4, but their scores leveled off over time, while earlier-adopted children’s scores remained the same. Greater average levels of externalizing problems in childhood predicted ADHD diagnosis and running away from home. Lastly, youth with lowest internalizing and externalizing scores in childhood reported currently using marijuana occasionally, while higher internalizing and externalizing scores predicted both abstinence and frequent use of marijuana. These results indicate that pre-adoptive risk factors and childhood behavior problems are salient predictors of some, but not all, indicators of mental health in adolescence and young adulthood. Findings on marijuana use support past literature revealing that adolescents who experiment occasionally with marijuana are better adjusted, beginning in childhood, than their abstaining or heavy-using peers (Shedler & Block, 1990). These findings indicate that even in a sample with majority (95%) prenatal substance exposure, some experimentation with marijuana is normative