Exposure to alcohol and illicit drugs during early adolescence has been associated with poor outcomes in adulthood. However, many adolescents with exposure to these substances also have a history of conduct problems, which raises the question of whether early exposure to alcohol and drugs leads to poor outcomes only for those adolescents who are already at risk. In a 30-year prospective study, we tested whether there was evidence that early substance exposure can be a causal factor for adolescents' future lives. After propensity-score matching, early-exposed adolescents remained at an increased risk for a number of poor outcomes. Approximately 50% of adolescents exposed to alcohol and illicit drugs prior to age 15 had no conduct-problem history, yet were still at an increased risk for adult substance dependence, herpes infection, early pregnancy, and crime. Efforts to reduce or delay early substance exposure may prevent a wide range of adult health problems and should not be restricted to adolescents who are already at risk.