We investigated direct and shared effects of family functioning and self-concept on the severity of adolescent externalizing problems in a sample of 224 clinically referred adolescents. Structural equation modeling (SEM) revealed strong, direct relationships between problem behaviors and both family functioning and self-concept. Using R. M. Baron and D. A. Kenny's (1986) and G. N. Holmbeck's (1997) criteria for testing mediation in SEM, family functioning partially mediated the relationship between self-concept and problem behaviors. A moderation model, testing the relationship between externalizing problems and the interaction between family functioning and self-concept, did not yield a significant effect. Our findings indicate that self-concept and family functioning exert direct and shared effects on externalizing problems and suggest that interventions for clinically referred adolescents should target both the individual adolescent and his/her family.