The goal of the study was to examine individual changes in substance dependence symptoms (alcohol, nicotine, and cannabis) over time and to examine how differences in change related to group membership. Participants included adolescent boys age 11 through 17, of which 36 were early-onset delinquent, 86 were late-onset delinquent, and 25 were nondelinquent boys from a large epidemiological twin sample. Early-onset delinquency is associated with earlier onset of substance abuse disorders (SUDs). Early starters have more severe behavioral problems than late starters. Early starters also are more likely to display severe antisocial behavior and adult offending. Early starters have an earlier affiliation with antisocial peers than late starters. Early starters were expected to be at greater risk for developing substance dependence problems than late starters and controls. Study data largely support those expectations. Tables, figure, references