Objective: The current study explores three avenues in early young adulthood through which adolescent problems may be linked to later substance use problems: problematic substance use, failure to assume adult roles and responsibilities, and exposure to pro-drug social influences. Method: Participants (N = 1,986; 49% female) filled out surveys at ages 18, 23 and 29. Participants were 67% white, 9% black, 10% Hispanic and 8% Asian. Deviance, poor mental health, substance use, alcohol and other drug (AOD) problems, and school drop-out were measured at age 18. AOD problems were also measured at age 23, as were role changes (e.g., marriage) and pro-drug social influences (e.g., friends use drugs). Indicators of substance abuse and dependence were measured at age 29. Demographics and family history of AOD were covariates. Results: Reporting more deviant behavior and heavier drinking at age 18 was associated with a higher likelihood of abuse and dependence at age 29. Alcohol use and pro-drug social influences at age 23 appeared to mediate the effects of adolescent substance use; lack of role assumption did not. The effect of poor mental health at age 18 was not mediated by any set of variables but instead appeared to directly predict dependence at age 29. Conclusions: Findings highlight the importance of early young adult drinking and substance-using peers in continuing patterns of heavy substance use developed during adolescence and also underscore the long-term impact of poor mental health during adolescence on substance use problems in late young adulthood. (Contains 2 tables and 1 figure.) [This article was reprinted from Alcohol Research Documentation, Inc.'s "Journal of Studies on Alcohol" (now called "Journal of Studies on Alcohol and Drugs"), Volume 66, Number 6, November 2005, pp. 766-775.]