Project Summary: Understanding co-occurring alcohol use disorders (AUDs) and internalizing disorders has become critically important as researchers consistently find high rates of comorbidity in adolescents and adults and continue to identify the adverse emotional, physical, and economic consequences that these disorders have. Despite these alarming findings, the connection between AUDs and internalizing disorders is not fully understood. Developing a better understanding of the course and connection between these disorders is an essential first step in the process of developing effective and timely assessments, prevention efforts, and treatments needed to address these harmful disorders. One proposed model of the relationship between these disorders, the Secondary Internalizing Disorder Pathway, posits that AUDs influence or provoke the development of internalizing disorders. Unfortunately, current research support for this pathway is mixed and many questions regarding the associations between AUDs and internalizing disorders remain. Since both alcohol use and internalizing disorders escalate in onset between adolescence and young adulthood it is imperative that the course and connection between these disorders be examined during this time period;however, few studies on this topic have included adolescents as they progress into young adulthood. This proposal aims to address these gaps in the literature by conducting a detailed test of the Secondary Internalizing Disorder Pathway in a unique longitudinal dataset including two cohorts: 1) A clinical sample of adolescents with AUDs but no prior evidence of internalizing disorders and 2) a sociodemographically comparable, family history of alcoholism matched, sample of community adolescents with no AUDs or internalizing disorders at baseline. These cohorts, followed semiannually for 10 years, afford the opportunity to examine the degree to which varying levels and longitudinal patterns of alcohol and other drug use provoke and relate to changes in internalizing symptoms and disorders. The present proposal will address foundational questions that remain unanswered and build upon these questions with innovative hypotheses. Specifically, Aim 1 will test the Secondary Internalizing Disorder Pathway in the clinical cohort. Aim 2 will test the same pathway in the community cohort and in doing so determine whether similar alcohol/substance use and internalizing symptom and disorder patterns emerge across samples. Aim 3 will further explore the same pathway in a developmentally sensitive fashion by investigating the impact of accelerations in and timing of alcohol/substance on internalizing symptoms and disorders as youths age from adolescence into emerging adulthood. In concert, results will have implications for understanding the relationship between alcohol and substance use problems and the emergence of internalizing symptoms/disorders as well as the development of treatment for these co-occurring problems.