A 3-month-old female patient suffering from poor peripheral circulation and paleness for 1 day was diagnosed with a congenital mesenteric defect with internal herniation. A plain abdominal x-ray revealed dilatation of bowel loops with ileus, while a lateral abdominal x-ray demonstrated the presence of several air-fluid levels. Abdominal ultrasonography revealed dilated, fluid-filled bowel loops. Abdominal CT revealed diffuse dilatation of the small-bowel loops. These findings led to the diagnosis of a congenital mesenteric defect with internal herniation. Exploratory laparotomy with segmental resection of the small intestine and an enterostomy was performed. Follow-up involved weekly visits to our outpatient department. The patient's daily activities and feeding status had returned close to normal after 1 month. No further signs of ileus were noted thereafter.