Undernutrition is a relatively common clinical condition, which may accompany or follow acute or chronic illness, faulty food habits, indigestion or any type of underfeeding. It is seen in combination with many pathologic conditions in varying degrees of severity. There are few diseases in the course of which the diet is not restricted at one time or another, either by the physician or involuntarily by the patient. It is not possible to differentiate the various grades of undernutrition definitely, because of the great number of individual variations in type of body build. The only method which offers any means of comparison is based on the relation of the weight to the expected weight for the height. Although this method is open to criticism, it serves a useful purpose until a better one is devised and probably gives a fairly accurate picture of the physiologic state of the child.