Objectives: To examine whether peer support and illness representation mediate the link between family support, self-management and well-being. Method: Fifty-two adolescents (12-18 years old) with Type I diabetes were recruited and followed over 6 months, completing assessments of self- management, well-being, and social support. Results: Perceived impact of diabetes and supportive family and friends were prospectively predictive of participants' well-being measures. Although support from family and friends was predictive of better dietary self-care, this relationship was mediated by personal model beliefs. In particular, beliefs about the effectiveness of the diabetes treatment regimen to control diabetes was predictive of better dietary self-care. Conclusions: Both friends and family are important to support adolescents as they live with and manage their diabetes. Personal models of diabetes are important determinants of both dietary self-care and well-being. In addition, personal models may serve to mediate the relationship between social support and dietary behavior.