The causes and symptoms of duodenal obstruction by compression at the superior mesenteric root are illustrated by four case histories. In two the symptoms were completely relieved by side-to-side duodenojejunostomy. In the other two, it was found that barium readily passed the site of obstruction when the patient was in the prone position, so that medical management sufficed; it consisted in complete bed rest, elevation of the foot of the bed, assumption of the knee-chest position after meals, and the wearing of a well-fitting abdominal support.