Ileosigmoid knot is one of the causes of intestinal obstruction, but it is very difficult to make a correct preoperative diagnosis of the disease. This rare condition with high mortality is usually found in adult patients and has rarely been reported in children. We recently experienced two patients with ileosigmoid knot. One was a 4-year-old boy and the other a 60-year-old man. Both patients had suffered the sudden onset of abdominal pain. The boy was in a state of shock on admission. Abdominal computed tomography findings indicated intestinal obstruction. In laparotomy, intestinal resection and detorsion without resection were performed for the boy and adult patients, respectively. We herein report a case of ileosigmoid knot in which the patient was the youngest reported in the English literature, and showed that the computed tomography examination provided valuable information in both patients.