Ulcerative colitis (UC) represents a risk factor for colorectal cancer, but the association between UC and appendix cancer is uncommon. A 60-year-old woman with a 5-year history of UC initially received medical treatment with mesalazine and prednisone with no satisfactory response; therefore surgery was indicated. The procedure was a total intersphincteric proctocolectomy with ileostomy. Histopathological analysis indicated adenocarcinoma from the cecal appendix, and chronic-active ulcerative colitis of the colon. In conclusion, surgeons and pathologists should examine every surgical specimen from patients with UC because of the possibility, although remote, of a neoplasic pathology. The appendix adenocarcinoma and ulcerative colitis may or may not be associated, same as colon cancer in patients with UC.