OBJECTIVE MPC located in the upper urinary tract is rare with only 2 cases reported to date. We report clinical and histopathological data on 26 patients to increase the knowledge of this rare entity. METHODS A clinical and histopathological review was performed in 943 patients with a neoplasm in the renal pelvis or ureter, diagnosed between 1971 and 1998. We identified 26 patients with MPC. No patients were alive at the end of the study. RESULTS Of the patients 11 had greater than 50% MPC and 15 had focal MPC (at least 10%). The incidence was 2.8%. Median patient age at diagnosis was 69 years (range 54 to 88) and the male-to-female ratio was 17:9. All except 4 patients had stage T3 disease or higher. Carcinoma in situ was identified in 64% of cases and vascular invasion was present in 81%. A total of 20 patients (77%) died of disease and only 7 survived longer than 5 years. CONCLUSIONS The prognosis is poor since most patients with MPC of the renal pelvis and ureter initially present with advanced disease. Stage for stage the prognosis is not different from that in nonMPC urothelial cell carcinoma. Surgery is curative in less advanced cases. However, radiotherapy and systemic chemotherapy appear to be ineffective.