Among the conditions in pediatric Amedicine requiring emergency care, intestinal obstruction due to congenital defect is one of the most frequent. Atresias, stenoses, intestinal duplications, annular pancreas, and meconium ileus have received considerable attention in surgical, pediatric, and radiological literature. Volvulus of the midgut, even though it demands the greatest expedition in treatment, has less often been the subject of reports. There are excellent discussions in the textbooks of pediatric surgery (Gross, 7; Swenson, 12) and in several authoritative papers (Ladd, 8; Mcintosh, 9; Gardner, 6; Dott, 4; Del Junco, 3), but the clinical and radiological pictures, and especially the potentially disastrous nature of this condition, are not as widely recognized as they must be if results are to be improved. In the present paper the essentials of the developmental background will be reviewed, and the clinical and radiographic findings in 36 cases seen at the Denver Children's Hospital during the last fifteen years will be reported. Cases of chronic partial duodenal obstruction from bands associated with malrotation and possible intermittent volvulus are not included. Pathologic Anatomy The midgut is that part of the intestine supplied by the superior mesenteric vessels. It extends from the distal duodenum to the mid-transverse colon. Midgut volvulus occurs as a result of malfixation of the colon and of the base of the small bowel mesentery. The colon and small bowel are then free to swivel on the superior mesenteric axis; when they twist far enough, the bowel becomes obstructed. With further tightening, vascular obstruction and infarction may occur. The developmental basis for malrotation and malfixation of the midgut was first described by Mall in 1898. In 1923 Dott (4) applied this knowledge to the clinical problem of volvulus and intestinal obstruction. Gross (7) and Swenson (12) give excellent reviews of the development of the malformation. Basically, early in embryonic life the gut is a straight tube with a flat dorsal mesentery (Fig. 1, A). As it outgrows the abdominal cavity, it bulges anteriorly into the fetal umbilicus. At eight weeks it has made a single loop, turning about 90° counterclockwise. In a few more weeks it returns into the abdomen and rotates counterclockwise again until it has turned about 180°. The area of the duodenojejunal juncture goes to the left of the midline behind the mesenteric vessels, while the cecum rotates around to the right and finally descends into the right lower quadrant. The mesentery becomes fixed from the ligament of Treitz to the right lower quadrant, and the colon attains its normal attachments (Fig. 1, B). Beattie (1) classified the maldevelopmental conditions according to the stage at which the defect occurred. Thus, omphalocele results from failure of regression of the bowel out of the umbilicus in the first stage.