A case of adenocarcinoma of the renal pelvis is presented. The patient was an 84-year-old man suffering from long-standing right-sided nephrolithiasis. Surgical resection of the right kidney revealed adenocarcinoma with slight stromal invasion. A tubulovillous adenoma, which was morphologically similar to an adenoma of the large intestine, was also found adjacent to the adenocarcinoma. The pelvic epithelium neighboring the lesion revealed intestinal metaplasia. Histochemical studies revealed that the tumor in the patient and adenocarcinomas or adenomas of the large intestine have similar properties of cytoplasmic mucin. These findings suggest that the epithelium with intestinal metaplasia may have developed into the adenoma and finally transformed into the adenocarcinoma. In addition, only tumor cells with severe atypia, most of which morphologically corresponded to adenocarcinoma, demonstrated positive nuclear staining for anti-p53. This suggests that p53 may play an important role in the malignant transformation of adenomas into adenocarcinomas, as is the case in the large intestine.