While fifty years ago 20 p. 100 of cystic fibrosis patients only reached the age of one year, more than 50 p. 100 of the patients now live more than twenty years. The clinical manifestations of cystic fibrosis are more diverse in adults than in children, so that the diagnosis might concern several specialties. In actual fact, only 3 to 7 p. 100 of cystic fibroses are diagnosed after thirteen to sixteen years, and in half the cases the symptoms had been present before the age of one year. In adults, the respiratory manifestations of cystic fibrosis are predominant, whereas the gastrointestinal manifestations tend to be blurred. Radiography of the chest shows interstitial lesions (opacities, cystic images, disorders of ventilation), principally located in the right side and the apex. The most common functional defect is an obstructive syndrome corresponding to a gradual involvement of the peripheral airways. A number of complications may develop, including recurrent Pseudomonas infection of the lung, pneumothorax, heart failure, malnutrition, liver cirrhosis, episodes of intestinal occlusion, etc. The longer life span of these patients raises the problems of diabetes with its vascular complications, infertility or pregnancy, social and professional insertion, and so forth. The prognosis of cystic fibrosis in adults depends on the date the diagnosis was made, on the therapeutic follow-up and on the creation of specialized centres. The control of Pseudomonas infections and the development of lung transplantation are the main advances to be expected.