A 3-year-old boy presented with complaints of acute abdominal pain. The patient had visited the primary care pediatric clinic the day after the onset and been diagnosed with viral gastroenteritis and received medication conservatively. However, the abdominal pain persisted, so the patient was referred by his primary care physician to the previous local hospital. An abdominal X-ray did not show dilation of intestine and findings of ileus. The patient underwent contrast-enhanced computed tomography (CT), which revealed a cystic lesion similar to the structure of the gastrointestinal tract and ascites retention in the abdominal cavity. The patient was therefore transferred to our hospital for acute abdomen. He had a fever and showed abdominal distension and tenderness with peritoneal signs in the right lower abdomen. Blood sampling showed an elevated white blood cell count and CRP. We reviewed the contrast-enhanced CT findings again. There were no findings of ileus or intestinal dilatation except for the cystic luminal structure. The blood supply of the entire gastrointestinal tract was also preserved, except for the cystic luminal structure. Based on the clinical symptoms and these imaging findings, the preoperative diagnosis was torsion of Meckel’s diverticulum. We decided to perform exploratory laparoscopic inspection to obtain a definitive diagnosis. Exploratory laparoscopy revealed that the dark-colored twisted cystic luminal structure was located at the right lower abdomen, and its root seemed to be continuous with the small intestine. After releasing the 720° clockwise twisting, the cystic luminal structure was confirmed to have branched off of the small intestine. However, the connected formation was not that of Meckel’s diverticulum, but rather duplication. Small-scale laparotomy using the umbilical trocar wound was then performed to clarify the pathophysiological mechanism. The entire small intestine was extracted through the wound retractor. A long segment of tubular ileal duplication was recognized at 120 cm from the oral side of the ileocecal region. The long-segment tubular ileal duplication shared the anti-mesenteric side of the intestinal wall along one-third of its length. The residual two-thirds of its length was free from the ileum and twisted in a manner similar to Meckel’s diverticulum. Thin pedicle-like structure was recognized at the root of duplication cyst. Blood supply was thought to be kept by both thin pedicle and intramural blood flow. The diverticulum-like part was necrotic due to the twisting. The intraoperative diagnosis was torsion of intestinal duplication. The duplicated portion was resected along with the normal ileum, and intestinal anastomosis was performed with one layer. An abdominal drain was not placed, and the wound was closed in layers. The excised specimen is shown in Fig. a. The pathological findings revealed that the luminal structure shared a muscular layer with the normal ileum and had an inner surface covered with intestinal epithelium, which was compatible with intestinal duplication, as shown in Fig. b and c. The postoperative course was uneventful, and the patient left our hospital on postoperative day 14. He showed no adverse events in 3 years of follow-up.