Many hospitalized patients are malnourished and the relationship between malnutrition, and outcome is well established. To determine which patients are at nutritional risks clinical scores are probably more accurate than evaluation using a single nutritional parameter. Among the numerous scores published, the Nutrition Risk Index and the Subjective Global Assessment are both well validated. One is based on objective measurements, whereas the second is based on medical history and physical examination. Effects of malnutrition on clinical outcome have been particularly well-demonstrated in surgical patients, and it is now recommended to treat malnutrition before surgery. In medical patients malnutrition has also been demonstrated to be predictive of poor outcome. Moreover it induces an increase of the diagnosis-related group length of stay and hospital charges. To prevent and to treat malnutrition is now essential and nutrition teams are needed in hospitals.