Omental cyst is a rare lesion occurring primarily during childhood and young adulthood. It is closely related to mesenteric and retroperitoneal cysts, all conditions most likely being of congenital or benign neoplastic lymphatic origin. Omental cysts usually present as abdominal distention of long duration, less frequently as a palpable abdominal mass. Rarely they cause an acute abdominal surgical crisis clinically resembling appendicitis with peritonitis. Two cases are reported, one with acute and one with chronic symptoms. The clinical and radiologic features of omental cyst are reviewed in order to increase awareness of this entity.