The circumstances leading to the diagnosis of cystic fibrosis are sensibly going to be modified in France, with the generalisation of systematic neonatal screening. Indeed, close to 95% of patients will be diagnosed in the neonatal period. Those who are missed by this screening often have a form of disease that is said to be moderate, with specific mutations, and without pancreatic insufficiency. However be the mode of revelation, the diagnosis should be confirmed by a positive sweat test with an elevated level of chlorine, and (or) the presence of 2 mutations in the gene causing the illness. Early diagnosis by screening only makes sense if the patients are followed in specialised centres of care, accredited by the professional bodies. It is in all likelihood to be at this price that the results, in terms of median survival, will improve in our country.