PURPOSE: To examine the role of family environment and peer networks in abstinence outcomes for adolescents 1 year after intake to alcohol and other drug (AOD) treatment. DESIGN: Survey of 419 adolescents 13 to 18 years of age at consecutive intakes to AOD treatment programs at four sites of a large health system, with telephone follow-up survey 1 year after intake. METHODS: Examined association of 1-year abstinence with baseline characteristics. Using logistic regression, we examined characteristics predicting 1-year abstinence and predicting having fewer than four substance-using friends at 1 year. RESULTS: We found that family environment scores related to family conflict, limit setting, and positive family experiences, were not related to abstinence outcomes, but peer networks were related. Adolescents with fewer (less than four) AOD-using friends were more likely to be abstinent than those with four or more AOD-using friends (65% vs. 41%, p= .0002). Having fewer than four AOD-using friends at intake predicted abstinence at 1 year (odds ratio [OR]= 2.904, p= .0002) and also predicted having fewer than four AOD-using friends at 1 year (OR= 2.557, p= 0.0007). CONCLUSIONS: Although family environment is an important factor in the development of AOD problems in adolescents, it did not play a significant role in treatment success. The quality of adolescent peer networks did independently predict positive outcomes. CLINICAL RELEVANCE: For physicians, advanced practice registered nurses, and other primary and behavioral care providers who screen and care for adolescents with AOD and other behavioral problems, our finding suggest the importance of focusing on improving the quality of their peer networks.