Annular pancreas is an interesting anomaly, the rarity of which has received adequate attention in the literature. In view of its strategic position, encircling the second portion of the duodenum, the infrequency of its identification during life is particularly remarkable. By this level pass all ingested food and fluids, and into this segment of the bowel are emptied the products of the liver, gallbladder, and pancreas. That the development of the pancreas may be somewhat haphazard, or at least irregular, is evidenced by the frequent finding of ectopic islands of pancreatic tissue in other nearby organs, notably the duodenal and gastric walls, and by the multiplicity of abnormal types of duct formation and their divers points of entry into the duodenum and even into the stomach (1). According to embryologists, the human pancreas arises as two entodermal outgrowths, the dorsal and ventral anlagen. The dorsal extends out from the posterior wall of the intestinal tube just proximal to the common bile duct. From this is formed all of the pancreas except a section of the head. The ventral anlage, from which the latter arises at first consists of two buds—a right and a left. The left normally atrophies quite early in embryonic life. As the intestine develops and rotates, it carries with it the ventral anlage and this ultimately fuses with the dorsal. The duct systems in the two sections also unite. The dorsal anlage provides the duct of the body, tail, and part of the head, while the remainder is derived from the ventral. It is obvious that any failure or delay in the development or rotation of the gut and its accompaniments may cause some type of anomaly. As Lehman (2) suggests, failure of the left bud of the ventral anlage to atrophy may be a cause of serious developmental irregularity. Dozzi (3) also considers this a likely possibility. In 1933, a complete review of the literature on annular pancreas was presented by McNaught (4), who by the inclusion of a case of his own brought the total number of recorded examples to 40. Two years later, with Cox (5), he reported a second case and added 3 more from the literature. In 1942, Lehman (2) brought the list up to 49, including a case of his own. Reports by Chapman and Mossman (6), Stofer (7), Gross and Chisholm (8), Custer and Waugh (9), Goldyne and Carlson (10), Nedelec (11), Brown, Bingham, and Cronk (12), Burger and Alrich (13), Ohlmacher and Marshall (14), Ravitch and Woods (15), Conroy and Woelfel (16), Haden (17), Bickford and Williamson (18), Anderson and Wapshaw (19), Payne (20), and Baker and Wilhelm (21) had brought the total by the end of 1951 to over 60. Anatomy: An annular process of pancreatic tissue extends from the head of the pancreas and encircles the duodenum as a thick band. Sometimes the ring is not quite complete on the anterior aspect (19). This variation is uncommon and is, of course, less constricting than complete encirclement.