We report a case of primary omental torsion which is a relatively care entity, together with a review of 59 cases in Japanese literature. A 47-year-old woman was admitted to the hospital because of right lower abdominal pain. On physical examination, tenderness, Blumberg signs and muscular defence were noted in the right lower abdomen. On a blood analysis, the white blood cell count and CRP increased to 10, 000/ul and 5.0mg/dl, resectively. Emergency laparotomy was performed under a diagnosis of acute appendicitis. A moderate amount of serosanquinous ascites and torsion of the greater omentum were found in the abdominal cavity. The twisted omentum about three turns was resected. We reviewed 59 cases of primary omental torsion reported in Japan including this case. It is generally difficult to diagnose primary omental torsion preoperatively. When we encounter a patient manifesting similar symptoms to those of acute appendicitis without gastrointestinal symptoms, whose abdominal ultrasonography showed no prominent findings of appendicitis, abdominal CT must be conducted to confirm the presence of abnormalities in the mesentery and intraabdominal fatty tissues.