The objective is to create for the Italian CF population reference values of the glucose, insulin and c-peptide concentrations in response to OGTT, and of model-derived parameters of insulin secretion and insulin sensitivity. This investigation should provide a better definition of the relationship of insulin secretory defects with age, sex, pancreatic insufficiency, liver disease and new CF therapies. Previous single-center experience (Milan) will be shared with centers from Central and Southern Italy in order to collect the largest number of patients. National parameters will allow to predict future CFRD, nutritional and respiratory decay and to set a rational basis for treatment.