It is rare that malrotation of the intestine in adult is diagnosed preoperatively. A 27-year-old man visited a hospital with anorexia and vomiting. First, he was diagnosed as having duodenal obstruction by ultrasonographic examination and CT scanning, and he was treated with stomach tube conservatively. However, a duodenography revealed a stenosis of the third portion of duodenum, and an angiography revealed branches of small intestine occuring from the right side of superior mesenteric artery, and colonic branches from the left side. Finally, malrotation of the intestine was diagnosed. The patient was sent to the hospital for operation. Intraoperative findings showed correct position of the colon, torsion of the small intestine clockwise by 180 degree around the axis of ileum about 10cm distant from the terminal ileum by strangulation occuring at the middlemesenterium of transversus colon, and stenosis of the duodenum. The torsion was reduced, and the stranguration was dissected. The small intestine was arranged to right side, the colon to left side, and an appendectomy was performed. It was considered a case of malrotation by 180 degree in Kakuda's classification. In the case of ileus of upper gastrointestinal tract, this disease must be kept in mind as a probable differantial diagnosis.