AS COMPARED with other portions of the gastro-intestinal tract, particularly the colon and duodenum, diverticulum of the stomach is usually considered as a relatively rare condition. Tupper (1), who reviewed the literature in 1923, could find only 37 cases described and to these he added one of his own. He credited the original description to Helmont, in 1804, but most of the cases have been reported since the use of roentgen rays, particularly during the past twenty years. Likewise, Nauwerck (2), in a review of the material from about 15,000 autopsies, could find but two cases, and other writers comment on the extremely infrequent occurrence of this condition. As with other supposedly rare lesions it is probable that many cases have been diagnosed by radiologists but have never been reported. At a meeting of the x-ray section of the Wisconsin State Medical Society, in 1931, when this subject was up for discussion, Dr. Frank Mackoy, of Milwaukee, stated that he had records of twelve cases and several other radiologists present had each seen one case. To my knowledge, none of these have been published. It is very likely, therefore, that the reported cases represent only a portion of those diagnosed. In the diagnostic x-ray section of the Department of Radiology of the University of Wisconsin, six cases of gastric diverticula have been observed. During the four years in which these were seen, approximately 5,000 patients have been examined by means of a barium meal. This gives an incidence of 0.12 per cent, or slightly more than one case per thousand. During this same period four cases of Zenker's pharyngoesophageal diverticulum have been observed, giving some idea of the relative frequency of these conditions as found in this clinic. Classification and Etiology As with diverticula elsewhere, those occurring in the stomach may be classed as either true or false. The true diverticulum consists of an out-pouching of the gastric wall and contains all of the coats of the stomach, although these may, at times, be considerably thinned out. The false diverticulum consists of a herniation of one coat through a tear or hole in another, usually the mucosa through the muscularis. One may also consider diverticula as being either of congenital or acquired origin. The latter might be of either the traction or pulsion type. In a majority of the reported cases the location has been in the cardiac end of the stomach, practically all of these having occurred on the posterior wall near the cardiac orifice. In the remaining cases, the location has been in various parts of the body and antrum of the stomach, there being no particular site of predilection. In this latter group are cases due to hair balls or other foreign bodies in the stomach, traction diverticula due to adhesions, a few with myomas in the walls, and a few showing remnants of pancreatic tissue. The etiology of this last group is uncertain but they may be congenital.