This study evaluated bidirectional associations between substance use, aggression, and delinquency across sixth, seventh, and eighth grades using data available from a large study of urban minority youth (n = 2,931). Group-based trajectory analysis revealed trajectories of aggression, delinquency, and substance use which support the existence of both adolescent-limited and life-course persistent offenders. In addition, a pattern of decreasing aggression was observed during middle school. Clear temporal associations were observed between developmental changes in aggression, delinquency, and substance use. Notably, the decreasing aggression trajectory was as likely to be associated with high trajectories of substance initiation as was the high aggression trajectory. Furthermore, trajectories of delinquency were differentially associated with future substance use; however, substance use trajectories did not predict trajectories of delinquency. There were few gender differences in the developmental progression of these problem behaviors during middle school with only two exceptions, males were more likely to follow a trajectory of decreasing aggression and a trajectory of high stable delinquency. Evaluations of ethnic/racial differences in the trajectory group membership also revealed few differences. The results of this study provide important information regarding interconnections between developmental changes in problem behavior that occur during the middle school years, highlighting groups that may be missed via traditional analytic approaches that predict mean changes. Aggr. Behav. 37:161–176, 2011. © 2010 Wiley-Liss, Inc.