During the last few years a number of articles have appeared on the dilated duodenum of the adult, and this condition is now recognized as a definite clinical entity. The symptoms, signs and x-ray appearance give a rather definite picture. In the adult, the condition is usually the result of some embryonic band, malformation, adhesions or compression by mesenteric root and artery. Although the subject of dilated duodenum has not been touched on by the pediatrician, there is no physical reason why the same picture might not occur in the infant and child. The case which will be reported here is one of constriction of the duodenum due to malformation and compression by the root of the mesentery. The history is typical of that of a dilated duodenum in the adult, and reemphasizes a more careful study of persistent vomiting in infancy and childhood and further dependence on the x-ray