This study examines the predictive significance of late adolescent substance use groups (i.e., abstainers, experimental users, at-risk users, and abusers) for early adult adaptation. Participants (N = 159) were drawn from a prospective longitudinal study of first-born children of low-income mothers. At 17.5 years of age, participants were assigned to substance use groups on the basis of their level of substance use involvement. At 26 years, early adult competence was assessed in the areas of education, work, romantic relationships, and global adaptation. Results indicate that 17.5-year substance use group membership significantly predicted high school completion, regular involvement in a long-term romantic relationship, good or better work ethic, and good or better global adjustment at 26 years when controlling for gender; IQ; 16-year internalizing and externalizing behavior problems, parental monitoring, and peer competence; and current substance use at 26 years. Group comparisons indicate that late adolescent substance use experimenters were significantly more likely in early adulthood to have (a) a high school diploma or higher level of education compared with abstainers (OR = 8.83); (b) regular involvement in long-term romantic relationships (OR = 3.23), and good or better global adaptation (OR = 4.08) compared with at-risk users; and (c) good or better work ethic (OR = 4.04) compared with abusers. This research indicates that patterns of late adolescent substance use has implications for early adult functioning in salient developmental domains.