During chronic diseases, malnutrition is found in approximately 40% of patients. Malnutrition is correlated with complication rates, handicap, need for care as well as mortality. Malnutrition can be related to two mechanisms: insufficient feeding and abnormal nutrient absorption or metabolism. Nutritional assessment of patients with chronic diseases should be helpful for the early detection and management of malnutrition. Nutritional supplementation was shown to improve both nutritional status and survival in selected conditions. Future therapies of malnutrition in chronic diseases rely to the selection of patients susceptible to respond to a new therapeutic approach which, depending on primary disease, may associate nutritional supplementation to rehabilitation and, in some conditions, anabolizing hormones.