Crohn's disease involves a great risk of malnutrition. Malabsorption, bacterial contamination, frequent abdominal surgery, meal-related pain, protein loss through the damaged mucosa contribute to creating nutritional problems. Malnutrition can worsen the outcome, both in medical and surgical patients, and deteriorate an often already altered immune response. Weight loss, low levels of blood protein, electrolytes, micronutrients and vitamins are usually related to the extension of the mucosal damage. Nutritional assessment can be difficult due to oedema and bleeding, who interfere with both clinical and laboratory evaluation. The exact amount of nitrogen, lipids, minerals stool loss can be useful. It is widely accepted the use of nutritional support in Crohn's disease, but many Authors do not agree concerning the route (enteral or parenteral) and the kind of nutrient to be used. Still controversial is the role of nutrition: just support or real therapy? Most recent hypothesis concerning the pathogenesis of Crohn's disease indicate food and/or bacterial antigens as involved in determining the pathology. The "bowel rest", considered for many years as a fasting period necessarily supported by parenteral nutrition, can also be obtained by the temporarily reduction or stop in presenting those antigens to the bowel mucosa. This new concept can be achieved not only by parenteral nutrition, but with an enteral elemental diet as well. The elemental diet contains all nutrients in the simplest way and thus succeeds in lowering or eliminating the antigenic power. The reported results seem to indicate an equivalence of enteral and parenteral nutrition; anyway enteral is advisable when feasible, being more physiological and less expensive and involving a lower risk of serious complications.(ABSTRACT TRUNCATED AT 250 WORDS)