A 77-year-old woman was admitted to the emergency department with chief complaints of upper abdominal pain and vomiting. Upper gastrointestinal contrast studies and irrigoscopy did not show any formation of the ligament of Treitz, and the small intestine had traveled to the right and the colon had traveled to the left from the duodenum. Abdominal contrast-enhanced CT showed a whorl-like pattern where the small intestine had rotated around the superior mesenteric artery. An obstruction site was noted in the vicinity of the transition from the duodenum to the jejunum. Duodenal obstruction associated with intestinal malrotation and midgut volvulus was diagnosed. The intestinal tract showed no blood flow impairment and no findings of strangulated ileus, so she underwent an elective laparoscopic Ladd procedure. Postoperatively, she showed no relapse of symptoms. Adult-onset intestinal malrotation is rare, and symptoms vary, so the question of whether laparoscopic surgery is indicated should be judged on a case-by-case basis.