While endometriosis is a common disorder in women of reproductive age, appendiceal endometriosis accounts for less than 1% of all pelvic endometriotic lesions. Involvement at this site may present as acute appendicitis and be diagnosed only upon postoperative histopathologic examination. We report such an occurrence of appendiceal endometriosis in a 40-year-old woman who presented with acute perforated appendicitis.