Transmesenteric hernia is a rare cause of small bowel strangulation in adults and, to our knowledge, no one has reported the existence of two mesenteric defects in an adult. Our patient was a 73-year-old Japanese woman who presented to our emergency department complaining of abdominal pain and nausea. Computed tomography with contrast enhancement revealed a closed loop obstruction in the pelvis, suggesting small bowel strangulation due to an internal hernia. The emergency exploratory laparotomy indicated a small bowel strangulation caused by a transmesenteric hernia. With the examination across whole parts of the mesentery, we identified another small defect. Both defects were closed by suture intraoperatively, and the patient's postoperative course was satisfactory. Searching for whole parts of the mesentery after the reduction of a hernia can help prevent the recurrence of internal hernias.