Introduction: Illness representations and psychological well-being were investigated in two patient groups diagnosed with insulin dependent diabetes; Type 1 diabetic patients, and patients with diabetes secondary to cystic fibrosis, a pre-existing, life threatening, genetic condition. The purpose of this study was to compare the illness representations held by patients to investigate whether differences in perceptions of consequences and control existed between groups. This study also investigated whether patients’ perceptions of illness played a role in levels of anxiety and depression and whether differences in illness representations existed between patients and their health care teams. Method: Participants completed self-report questionnaires measuring illness representations of diabetes and levels of anxiety and depression. All eligible participants were sent the study pack to their home address by post. A total of 22 cystic fibrosis related diabetes (CFRD) and 45 Type 1 diabetes patients completed and returned the questionnaires. Age, duration of diabetes and recent blood glucose level (HbAlc level) information was obtained for each participant. All participants were over 16 years of age. In addition, a total of 17 staff, working within the adult cystic fibrosis service completed an adapted version of the Illness Perceptions Questionnaire. Results & Discussion: There were no significant differences between the two patient groups on perceived consequences or treatment control of diabetes. Contrary to prediction, the CFRD group perceived significantly lower levels of personal control over their diabetes than the Type 1 group (p<.01). This finding may, in part, be due to the CFRD patients’ perception of their diabetes as a largely uncontrollable consequence of the progression of their cystic fibrosis. No associations were found between illness representations and levels of anxiety and depression in the CFRD group, however perceived consequences and treatment control were predictive of levels of depression, measured by the Well-being Questionnaire, in the Type 1 group (Adjusted R squared = .208, p= 0.016). Differences existed between the staff group and the CFRD patient group on perceived consequences of diabetes (<.001) but staff and patients beliefs converged on perceived levels of control. Clinical implications and future research recommendations are discussed.