We herein report a case of an internal hernia projecting through a mesenteric defect following laparoscopic-assisted colectomy to the lesser omental cleft in a 61-year-old female. We performed laparoscopic-assisted partial resection of the transverse colon to treat transverse colon cancer. Three years and 6 months after the operation, the patient developed a bowel obstruction requiring surgical intervention. When we observed the intraperitoneal space under laparoscopy, we determined that the small intestine had passed into the bursa omentalis through the mesenteric defect. Additionally, an abnormal opening of the lesser omentum was present with a portion of the small intestine escaping into the space inferior to the liver. We performed reintegration of the escaped bowel and closed the mesenteric defect laparoscopically. This is the first case of an internal hernia projecting through a mesenteric defect following laparoscopic-assisted colectomy that we have experienced out of more than 2400 cases. Further research is needed to identify the patients who would benefit from the closure of mesenteric defects during laparoscopic-assisted colectomy.

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