Of 426 operatively removed renal cell carcinomas, macroscopic vein invasion was proven in 197 cases,i.e. 46.2%. The inferior vena cava contained tumor in 4.0%, the trunk of the renal vein in 24.4%, and in 18.1 % only the major branches of the renal vein were found invaded. In 132 patients (31.0%) with tumor-free major renal branches, vein invasion could be demonstrated histologically. Statistically significant correlations could be found comparing renal vein invasion and other pathological parameters as histological grade, tumor diameter, local spread and lymphatic métastasés. Proof of renal vein invasion affects prognosis: age-corrected 5-year survival rates amounted to 33.6 ± 8.5% in macroscopically determined vein invasion; 62.3 ± 11.9% in histologically determined vein invasion, and 89.0 ± 10.3% without vein invasion. Vein invasion should be subdivided into an only histological and a macroscopical group of evidence, because significantly different survival rates will result. Therefore, an exact definition of the UICC classification criteria and a standardized usage are necessary and should be kept in mind for the next issue of the UICC classifications.