A model of the relation between self-concept and internalizing and externalizing problem behaviours in adolescence, with the self-concept influencing problem behaviours (S[right arrow]IE), was assessed using a sample of 277 Swedish adolescents. The model was tested in a path analysis with data from Youth Self Report (YSR) and Structural Analysis of Social Behaviour (SASB) questionnaires. Consistent with the model, a positive self-concept was found to be the most important factor for adjustment and for protection against common problem behaviour. A negative self-concept combined with female gender were risk factors for internalized problems. Self-control had only a direct effect on externalizing behaviour for boys. Adolescents of 15, 16 years of age had a stronger relationship between a negative self-concept and externalizing problem behaviour than younger and older adolescents. Internalizing problem behaviours such as anxiety and depression predicted aggressive and delinquent behaviour. These findings highlight the importance of promoting of a positive self-concept in every adolescent in various psychosocial contexts.