Primary omental infarction (POI) is a rare cause of acute abdomen. Most patients have aggravating abdominal pain without gastrointestinal symptoms. Here, we report a case of omental infarction in a 50-year-old woman, who had left abdominal pain and intestinal obstruction. Preoperative computed tomography (CT) of the abdomen showed a left ovarian cyst measuring 6.0 cm × 4.5 cm but otherwise seemed normal initially. The white blood cell count was 9.71 × 109/L, and D-dimer was 1.58 mg/L. Laparoscopic exploration was performed 1 day after admission because of peritonitis and intestinal obstruction. During the exploration, a segment of congested necrotic omentum was found adhering to the abdominal wall with a segment of small intestine. Bloody ascites was also observed in the abdominal cavity. We resected the nonviable segmental omentum, and the ovarian cyst was removed by the gynecologist using laparoscopic procedures. Final pathological findings confirmed POI. While reanalyzing the preoperative CT, a segmental fat mass with an increased density was noted in the left lower quadrant, which was consistent with the intraoperative view 6 days after surgery. The patient recovered uneventfully and was discharged.