Transomental hernia often develops into strangulated ileus. We report on an 81-year-old man with strangulated ileus due to transomental hernia, diagnosed preoperatively by abdominal CT. The patient was referred to our surgical division because of progressive abdominal pain and vomiting. He had no history of laparotomy. An abdominal CT scan showed dilated small intestinal loops with intraluminal air and strangulated small intestinal loops with engorged mesenteric vessels. We diagnosed this as a strangulated internal hernia due to transomental hernia and conducted an emergency laparotomy. The jejunum had herniated through an abnormal hiatus of the greater omentum to the peritoneal cavity. The strangulated intestinal loop, about 15 cm long, was released and the postoperative course was uneventful. In the absence of a previous laparotomy, the differential diagnosis of intestinal obstruction should include internal hernia. An abdominal CT scan is useful for the preoperative and prompt diagnosis of transomental hernia.