Adenocarcinoma of the appendix is rarely encountered and is usually discovered at the pathology examination of the surgical specimen. Adenocarcinoma of the vermiform appendix is a rare neoplasm and constitutes <0.5% of all gastrointestinal neoplasms. There is no symptom of appendiceal cancer, and it is very difficult to diagnose preoperatively. Most female patients are diagnosed as having a gynecologic disease. Second primary synchronous and metachronous neoplasms, especially in the gastrointestinal tract, are found in up to 35% of patients with appendix adenocarcinoma. We report a case of adenocarcinoma in a 56-year-old woman misdiagnosed as having right ovarian carcinoma, and we review the literature.