The significance of vessel invasion by cancer of the renal pelvis and ureter was estimated with surgical specimens of 45 patients. The vessel invasion by cancer was observed in 25 out of 45 cases (55.6%). The incidence of vessel invasion increased with the grade of cancer and the extent of the primary tumor. The postoperative metastases by cancer was noted in 22 of the 25 patients with vessel invasion (88%) and in 4 of 20 (20%) patients without vessel invasion. The incidence of metastases in patients with vessel invasion was significantly higher than that without it (p<0.01). The 5-year survival rate was 13.1% in the patients with vessel invasion and 80.6% in the patients without it (p<0.005). Postoperative chemotherapy had no effect on the unfavorable outcome of the patients with vessel invasion. Therefore, vessel invasion by cancer may be one of the prognostic factors in renal pelvic and ureteral cancer. The patients with vessel invasion should be treated with more aggressive therapy to improve the poor prognosis.