Prevention of malnutrition, a consequence of elevated energy requirements, increased losses and low caloric intake, is one of the main goals in the treatment of cystic fibrosis. Caloric stool losses, catch-up growth and an elevated energy expenditure, even in the absence of overt lung disease and malabsorption, have led to recommendations for a caloric intake of 120-150% of the recommended daily allowances. A high energy intake with a fat content of at least 40 calorie % and adequate pancreatic supplementation has shown to improve growth and median age of survival. As a rational treatment of the fundamental disturbance in cystic fibrosis, a decrease in chloride permeability across epithelia, is not yet available, treatment should be concentrated on adequate nutritional support in combination with optimal correction of those gastrointestinal abnormalities including faecal bile acid loss, small intestinal abnormalities, pancreatic insufficiency, hormonal abnormalities and disturbances in gastrointestinal motility, which may aggravate maldigestion and malabsorption.