Across developmental transitions, relationships with family, peers, and intimate partners can be contexts of risk or resilience. Ideally, these relationships protect and support positive adaptation to new roles, but sometimes they expose the individual to risk that is predictive of later problem behaviors, such as substance abuse. Our research team has developed an effective intervention that targets these key relationships in order to reduce substance use and other risk behaviors while simultaneously enhancing protective factors that lead to healthy, adaptive behavior. This intervention, called the Family Check-Up (FCU), has been studied across various ages and samples. We propose to now focus on the transition to adulthood, the period associated with the highest rates of substance use and life-threatening risk behaviors (e.g., high-risk sexual behavior, drinking and driving). This study will extend our previous work by offering the FCU as youth transition out of high school. It will examine how parent-child relationships in late adolescence may be protective or may contribute to escalating substance use and abuse typically observed during the transition to adulthood. We propose to follow up an existing community sample of 593 ethnically and socioeconomically diverse youth and their families who were originally recruited at age 11 as part of a school-based, family-centered intervention for substance use prevention during the middle school years. Families assigned to the original treatment condition will be offered an additional intervention that would target parent-youth relationships during this transition, and would provide critical information about developmental changes in family processes that protect youth from substance abuse during this period. The late-adolescence version of the FCU intervention is designed to (a) prevent escalation of substance use, (b) focus on parent-youth relationships that foster independent living, (c) discourage unhealthy peer relationships and activities that promote drug use, and (d) provide support to enhance adaptive behavior and healthy adult outcomes during the transition to adulthood. We will also evaluate the enduring efficacy of the FCU and the preliminary efficacy of the FCU for late adolescence in terms of reducing growth in substance use and problem behaviors and supporting healthy adaptation. The study will significantly contribute to our understanding of parenting in late adolescence and risk factors associated with substance use, as well as protective factors that lead to health and adaptive behavior in early adulthood. If successful, this intervention will be a cost-effective means to reduce substance use and other risk behavior that can be embedded into high schools as youth transition to independent living.