We present a rare case of strangulated closed loop small bowel obstruction secondary to a transmesosigmoid hernia to emphasize the diagnostic role of computed tomography in patients with no history of previous surgery. The characteristic computed tomographic features showed a cluster of dilated, fluid-filled, U- and C-shaped loops of small bowel entrapped the left posterior and lateral to the sigmoid colon through a defect in the mesosigmoid, which caused anterior and medial displacement of the sigmoid colon.