PURPOSE: To evaluate CT findings of internal hernia. MATERIALS AND METHODS: Three patients with internal hernia had abdominal CT scans and two of them had small bowel follow through examinations. The CT features of two patients with retroanastomotic and one patient with left paraduodenal hernia were evaluated and correlated with small bowel follow through examinations, and surgical findings. Two patients with retroanastomotic hernia had a history of subtotal gastrectomy with antecolic gastrojejunostomy. The diagnosis of internal hernia was made on the basis of surgical find ings in two patients of retroanastomotic hernia, and characteristic barium study findings in one patient of left paraduodenal hernia. RESULTS: The small bowel follow through examination showed small bowel loops gathered in a circumscribed mass in the left mid abdomen, and delay in passage through these loops. In case of left paraduodenal hernia, abrupt narrowing of the distal duodenum could be identified. The characteristic CT findings of all three patients were whorling of the mesentery and mesenteric vessels in the left mid-abdomen. In the patient with left paraduodenal hernia, after resolution of the gastrointestinal symptoms, a follow-up CT scan showed spontaneous disappearance of whorling of the mesentery and mesenteric vessels suggesting spontaneous resolution of the hernia. In the other two cases, upon exploration of the abdomen, dilatation of afferent duodenum caused by adhesion between ligament of Treitz and adjacent bowel walls, and retro- anastomotic herniation of the efferent loops were found. CONCLUSION: The usual diagnosis of internal hernia is based on the appearance of the small bowel follow through examination. However, we consider that the whorling appearance(we call it whorling sign) of the mesentery and mesenteric vessels on CT scan is also suggestive of internal hernia in patients under clinical suspicion.