IN this study of 310 cases of duodenal diverticula we have not only considered the radiologic aspects of the subject but we have also attempted to evaluate their clinical significance. No doubt every radiologist has had the following experience. After completing a gastro-intestinal series the only positive finding may be a diverticulum of the duodenum. The clinician will then want to know whether or not this pocket is the cause of the patient's symptoms, which may vary from mild indigestion to severe pain with vomiting or even hemorrhage. It is mainly to answer this question that we are presenting these data. Roentgenographically diagnosis should not be very difficult. The diverticulum is characterized by an extraluminal collection of barium communicating with the main duodenal stream by a stem of varying size. The pocket may be a few millimeters in size or, as Lockwood (1) reports, may become so huge as to contain 1,000 c.c. of fluid. Two of the largest in our series measured 7cm. in diameter. They may arise from any portion of the duodenum, most frequently from the internal or pancreatic border but occasionally from the external border or from the anterior wall. The mucosal pattern of the adjacent duodenum reveals its normal markings, but at the stem of the diverticulum the mucosa assumes a linear pattern. This aids in distinguishing it from benign or carcinomatous ulceration. The pocket itself occasionally may show poor quality, due to the displacement of the barium by food or mucus; and at times, in the vertical position a fluid level can be seen. The fact that approximately one-half of the lesions were not seen fluoroscopically is not of great significance, because in a teaching institution the examinations are performed by men of varying degrees of experience. In this connection it is interesting to note that we can usually gauge the ability of our residents by the number of diverticula which they discover fluoroscopically. Generally the lesions are found in proportion to the care with which the fluoroscopy is done. However, this statement must not be taken too dogmatically, because on several occasions, although the pocket was known to be present, a search by an experienced fluoroscopist failed to reveal it. In one instance a diverticulum was not seen on three different radioscopic examinations and was noted on only one of the sets of films. In another instance the pocket was not seen either fluoroscopically or on the films on two successive examinations. On the third examination it was visualized both roentgenoscopically and roentgenographically and there was a six-hour retention in the pocket. However, a fourth and fifth examination again failed to reveal the diverticulum.