A 76-year-old female patient with diarrhea and lower abdominal pain was found by barium enema to have an ileocecal tumor. Endoscopic appearance was suggestive of malignancy; however, biopsy revealed villous adenoma. Ileocecal resection was performed. Postoperative histological examination revealed multiple foci of carcinoma in situ within an adenoma extending along the entire appendix and obstructing its base. Twelve cases of early primary carcinoma of the appendix reported in the literature were reviewed, and the preoperative diagnosis and operative methods are discussed.