Present in 85-90% of patients, pancreatic exocrine insufficiency contributes to growth retardation and delayed puberty in the child, and low weight in the adult. The incidence of hepatic disease varies according to whether one considers the discovery of histological abnormalities at autopsy of patients who have died from other complications (20-70%) or the presence of a focal or multilobular biliary cirrhosis complicated or not by portal hypertension (2-10%). Gastro-oesophageal reflux can contribute to the degradation of the nutritional state and exacerbate the respiratory symptomatology. All deviations of anthropometric parameters (weight/height ratio, body mass index) from standard references are a warning sign and justify nutritional assistance, of which one distinguishes 3 successive stages by chronological order: fractionated oral supplementation, nasogastric enteral nutrition and parenteral nutrition.