ABSTRACT BACKGROUND: Diabetes is a common complication in adults with cystic fibrosis. Patients with cystic fibrosis experience a deteriorating pulmonary function and nutritional status in the period preceding onset of diabetes. Insulin improves pulmonary function and nutritional parameters in patients with cystic fibrosis-related diabetes. OBJECTIVE: Review literature in order to investigate the influence of insulin on pulmonary function, nutrition and clinical status in patients with cystic fibrosis prior to onset of diabetes, and evaluate recommendations for such treatment. METHODS: This assignment is based on a review of relevant studies in the Pubmed database. RESULTS: There is to date no large controlled studies investigating influence of insulin in cystic fibrosis patients prior to onset of diabetes. CONCLUSIONS: There is to date no conclusive data regarding influence of insulin in cystic fibrosis patients during the period preceding onset of diabetes. Treatment with insulin during this phase of the disease has to be considered individually.