From socialization theory, it was hypothesized that parental support and monitoring as well as peer deviance would influence individual trajectories of alcohol misuse, other substance use, and delinquency. Six waves of data were analyzed using interviews with 506 adolescents in a general population sample. Results from multilevel modeling showed that monitoring significantly predicted adolescents’ initial levels (intercepts) of alcohol misuse and delinquency. Parental monitoring strongly predicted the rates of increase (slope) in all 3 problem behaviors. Peer deviance significantly predicted initial levels of all problem behaviors and the rates of increase in them. This study provides evidence that both effective parenting and avoidance of associations with delinquent peers are important factors in preventing adolescent problem behaviors.