In a sample of 998 ethnically diverse adolescents, a multiagent, multimethod approach to the measurement of adolescent effortful control, adolescent substance use, and friendship influence was used to predict escalations to early-adult tobacco, alcohol, and marijuana use by ages 22-23. Structural equation modeling revealed that adolescent substance use and friends' substance use tended to be highly correlated and together were robust predictors of a problematic pattern of usage for all substances in early adulthood. In addition, the adolescent effortful control construct directly predicted progressions to problematic use of tobacco and marijuana, but not for alcohol. In the alcohol model, effortful control interacted with the construct of substance use lifestyle (based on adolescent alcohol use and friends' substance use) when predicting problematic alcohol use in early adulthood. Results held when comparing across genders and across ethnic groups. These findings emphasize the importance of addressing adolescent self-regulation in interventions designed to treat and prevent early-adult substance abuse.