This study set out to examine whether peer support and illness representation mediates the link between family support, self-management and well-being. Seventy-four participants (12-18-years-old) with type I diabetes mellitus completed questionnaires assessing their self-management, depression, anxiety, perceived social support and personal models of diabetes. Perceived impact of diabetes, but not perceived seriousness, and peer support were significant predictors of depression. Family support was a significant predictor of all self-management measures. However, for dietary self-management this relationship was partially mediated by the perceived efficacy of treatment to control diabetes, but not efficacy of treatment to prevent complications.