The influence of family management skills (i.e., supervision, discipline, and positive adult-youth relationship) and deviant peer association on youth antisocial behavior was examined within the context of a randomized clinical trial contrasting multidimensional treatment foster care and services-as-usual group care. Participants were male adolescents with histories of chronic and serious juvenile delinquency who were mandated into residential care by the juvenile court. As hypothesized, family management skills and deviant peer association mediated the effect of treatment condition and accounted for 32% of the variance in subsequent antisocial behavior.