Longitudinal data from 746 adolescents in Toronto, Canada (54% females), was gathered in eight waves over seven years (1995 through 2001), beginning when the youths were 10 to 12 years old (mean age = 11.8, SD = 1.2 years). Five trajectories of substance use were identified: chronic-high, childhood onset-rapid high, childhood onset-moderate, adolescent onset-moderate, and non-use groups. Late childhood risk factors for substance use included delinquency, academic disengagement, low parental monitoring, and associating with substance-using peers. Externalizing problems emerged as an additional risk factor for the most severe substance-using group during adolescence. Of note, the childhood onset-moderate group reported only moderate levels of substance use during adolescence despite high levels of risk during late childhood. Implications for prevention of and intervention for substance use are discussed.