An 85-year-old woman was admitted to our hospital because of appetite loss and vomiting. She had no previous history of abdominal surgery, trauma, or intra-abdominal inflammation. Following the diagnosis of a small bowel obstruction due to an incarcerated left inguinal hernia, manual hernia repositioning was attempted, and proceeded smoothly. However, 42 hour after the procedure, she suddenly developed abdominal pain without recurrence of the incarcerated inguinal hernia. Abdominal computed tomography revealed signs of small bowel strangulation; therefore, emergency surgery was performed 48 hour after admission. On laparotomy, a defect was found in the greater omentum, and a part of the ileum was incarcerated by the defect. The operative diagnosis was spontaneous transomental hernia. Incision of the greater omentum was performed, and no ischemic changes were observed in the ileum; therefore, bowel resection was not performed, and the left inguinal hernia orifice was repaired. The postoperative course was uneventful. The transomental hernia in our case might have been induced because of the incarcerated inguinal hernia. For patients plagued with persistent small bowel obstruction after successful manual repositioning of an incarcerated inguinal hernia, concurrent internal hernia should be considered as a possible cause of the persistent small bowel obstruction.