Diabetes is a frequent and serious complication in Cystic Fibrosis (CF) caused by defects in insulin secretion. New modulator therapies targeted at CFTR defect have become available raising hope to prevent or treat the CF-related diabetes (CFRD). Current evidence does not support significant effects, but the early natural history of insulin secretory defects according to CFTR genotypes is unclear: moreover researchers speculate that modulators have to be started in the first years of life before the endocrine pancreatic damage becomes severe. Therefore, by a collaborative multicenter perspective trial, a large number of 6-11 years old CF subjects eligible for CFTR modulators will be recruited. Among them, different study groups (starting treatment by modulators, non treated, already in treatment) will be monitored. Repeated OGTTs, as previously developed to assess the insulin secretion parameters, will be performed along with pulmonary, exocrine pancreatic and liver function and nutritional status assessment. The study results will fill important gaps in knowledge about CFRD.