Background: This study examines the longitudinal associations between adolescent tobacco and cannabis use and young adult functioning. Methods: Data for analysis come from the Ontario Child Health Study (OCHS), a prospective study of child health, psychiatric disorder and adolescent substance use in a general population sample that began in 1983, with follow-ups in 1987 and 2001. The sample for analysis includes 1,282 individuals who were between the ages of 12 and 16 years during the original OCHS in 1983 or the first follow-up in 1987 and returned for the 2001 follow-up. Results: Tobacco use in adolescence and continued use in adulthood is associated with increased risk for poorer functioning across multiple domains, including physical health and life satisfaction (0.62 and 0.66 standard units lower, respectively), depression (Odds Ratio = 3.44), personal income ($7,281 less per year) and years of education (2.29 years lower). Cannabis use is associated with a reduced set of adverse outcomes and the magnitude of the effects is weaker. Conclusions: The long-term risks associated with adolescent tobacco and cannabis use speak to the importance of prevention and early intervention.