Adolescence is a time of heightened risk for relatively intensive alcohol and other drug use behaviors. However, heavy use is often “adolescence-limited,” giving way to moderation or cessation in adulthood. We examined individual differences in risk factors at age 18 that were predictive of alternative alcohol and drug use trajectories from adolescence to adulthood. Data were collected prospectively on four occasions from participants in the Rutgers Health and Human Development Project. Subsets of individuals representing three prototypical trajectories of (1) consistently low alcohol and drug use during adolescence and early adulthood; (2) heavier alcohol or drug use during adolescence, but not during adulthood; and (3) persistent heavier alcohol or drug use from adolescence into adulthood were found to differ significantly on a number of intrapersonal, behavioral, and environmental risk factors, with the adolescence-limited group consistently scoring between the other two groups. Based on these results, a composite risk index was constructed. In the total sample, however, when the effect of alcohol and drug use behaviors at age 18 was controlled, the composite risk index was unrelated to adult (age 28 to 31) levels of alcohol and drug use and consequences. Thus, in this community sample, well-documented risk factors assessed in adolescence did not exhibit any direct, longterm effects on use intensity and problems in adulthood. It is concluded that the assessed risk factors (disinhibtion, cognitive structure, play, deviant coping, friends' deviance, and stressful life events) are not immutable, but subject to individual and normative changes during the transition from adolescence to adulthood. More research is needed to determine the long-term stability of risk factors, and how changes in risk factors over time, discontinuities in what constitutes risk in adolescence versus adulthood, and proximal adult protective factors that Compensate for early risk contribute to developmental patterns of use.