Primary signet ring cell carcinoma of the appendix is a very rare neoplasm that usually presents with signs and symptoms of acute appendicitis and in particular with a right lower abdominal pain. Preoperative imaging detection of appendiceal adenocarcinoma has an important value because it may result in an appropriate surgical procedure. We report a rare case of primary signet ring cell carcinoma of the vermiform appendix in an 80-year-old man who was misdiagnosed on computed tomography (CT) scan as acute appendicitis.