As the usual complications of gastric and duodenal ulcer are not simple but are intimately interrelated, a brief consideration of their nature and treatment as a single problem is of value. Some of the complications that occur are not always preventable, such as hemorrhage in an arteriosclerotic subject, alkalosis in a subject with damaged kidneys, or sudden perforation in a subject with acute ulcer of infectious origin. However, most of the complications that arise represent a breakdown of medical control and management, partly the fault of the physician in not sufficiently educating his patient in the nature and dangers of his ulcer but primarily that of the patient in failing to follow his instructions rigidly. Most of the complications considered here occurred in patients who were previously under some form of medical treatment that had not been sufficiently heeded. The person with peptic ulcer must be educated as to the