Two cases of primary adenocarcinoma of the renal pelvis are described. One patient was a 64-year-old female who had multiple papillary tumors in the right ureter and renal pelvis. The other was a 57-year-old male who had diffuse infiltrating carcinoma in the left renal pelvis with calculi. In both cases, the lining of the renal pelvis underwent columnar cell metaplasia and the tumor cells showed mucin production. Forty-six cases reported previously are reviewed briefly. The histogenesis of primary adenocarcinoma of the renal pelvis seems to be closely related to metaplasia of transitional epithelium induced by longstanding chronic inflammation or renal calculi in many cases.