Mucoviscidosis (cystic fibrosis of the pancreas) is the most frequent lethal genetic disorder in the white race. It is an autosomal recessive transmission. In spite of its recent localisation on the 7th chromosome, the fundamental mechanism responsible for the symptoms remains unknown and it is still a syndrome more than a disease. It presents as a generalised seromucous exocrinopathy. The serous glands are functionally abnormal and have secretions too rich in chloride which allows for the sweat test (the only test of diagnostic value). The accumulation of abnormal mucous secretions is responsible for the clinical manifestations: intestinal troubles, bronchial and pulmonary disease, progressive pancreatic insufficiency and biliary cirrhosis. Mucoviscidosis is not longer a disease exclusively of children. The treatment which is solely symptomatic has profoundly changed the prognosis. Half of the children afflicted become adults. This fact and the better condition of diagnosis explain the appearance of a new symptomatology sometimes with a late presentation. On the basis of the genetic and prognostic implications one should consider the diagnosis at any age even if the general state is well conserved. The diagnosis rests on the association of suggestive symptoms and a disturbed sweat test. In the adult the presenting signs are always respiratory, more rarely digestive, and sometimes sterility. These associations are very suggestive. The current evolution requires a specific clinical management of new adult cases who, even if not in a very good clinical state, maintains a vital hope for several years with symptomatic treatment (and the hope perhaps that the discovery of the fundamental defect will lead to more specific therapy).