Sigmoid mesocolon hernia is an uncommon type of internal hernia. A 63-year-old man who presented with pain in the left side of the abdomen and nausea was referred to our department for treatment of ileus. He was initially managed conservatively, but as his symptoms became progressively worse, a laparoscopy was done, which revealed hemorrhagic ascites and necrosis of the small intestine in the lower abdomen. An open laparotomy was subsequently performed and the intraoperative findings were consistent with a transmesosigmoid hernia. There was an abnormal defect in the sigmoid mesocolon and protrusion of about 30 cm of small bowel through this abnormal opening, which had resulted in strangulation of the bowel. The necrosed part of the intestine was resected and the defect was closed.