This study evaluated the adolescent tobacco-use trajectories that predict nicotine dependence in early adulthood and when these trajectories start to diverge. As part of a follow-up to a large prevention trial, the present study evaluated 1,017 individuals from early adolescence (age 12) to early adulthood (age 28). Participants were recruited from eight middle schools in Kansas City, Missouri. Students were entering 6th grade or 7th grade at baseline. Smoking was evaluated at baseline, 6 months, at annual follow-ups through high school, and every 18 months thereafter until age 28. The study goals were to determine (a) whether distinct weekly tobacco-use trajectories could be identified between early adolescence and emerging adulthood (ages 12-24); (b) when during development these trajectories diverged; and (c) which trajectories could predict nicotine dependence in early adulthood (ages 26-28). A four-trajectory mixed model (abstainers, low users, late stable users, and early stable users) demonstrated the best fit to the data. Membership in increasingly high-use trajectories placed participants at greater relative risk for becoming nicotine dependent than did membership in lower-use trajectories. General linear models showed greater weekly cigarette consumption for early stable users as early as the first wave of data collection (age 12) and significant differences among all other trajectories by age 15. The findings support the implementation of smoking prevention programs early in middle or junior high school and suggest that adolescents who are already smoking at least two cigarettes per week by age 12 may benefit from additional addiction prevention efforts.