Appendiceal carcinoma masquerading as primary bladder carcinoma. We report 2 cases of appendiceal adenocarcinoma invading the bladder. Both tumors masqueraded as primary bladder carcinomas. Cystoscopic biopsies obtained adenocarcinomatous tissue and the secondary nature of the bladder lesion became apparent at laparotomy in both cases. One patient was treated with surgical resection of the appendix, the adjacent cecal wall and the bladder wall, and postoperative irradiation. She was well 10 years later. The other patient was treated with right colectomy and segmental bladder resection. She died of diffuse peritoneal recurrence 6 years later. 