BACKGROUND The prognostic significance of venous tumor thrombus extension in patients with renal cell carcinoma (RCC) is a matter of many controversies in the current literature. OBJECTIVE To evaluate the prognostic role of inferior vena cava (IVC) involvement in a large series of pT3b and pT3c RCCs. DESIGN, SETTING, AND PARTICIPANTS A total of 1192 patients from 13 European institutions underwent a radical nephrectomy for pT3b and pT3c RCC between 1982 and 2003. The patients were evaluated in a retrospective manner. Age, gender, clinical symptoms, Eastern Cooperative Oncology Group (ECOG) performance status, TNM stage, tumor size, adrenal invasion, perinephric fat invasion, histological type, and Fuhrman grade were reviewed. The log-rank and Cox uni- and multivariate regression analyses were used to evaluate prognostic factors for overall survival. MEASUREMENTS Overall survival and prognostic factors for overall survival in patients with RCC extending to the renal vein (RV) or to the IVC. RESULTS AND LIMITATIONS The median follow-up was 61.4 mo (56.3-66.5 mo). The mean age was 63.2 yr. The mean tumor size was 8.9 cm. Group 1 (Gr 1) included 933 patients with a renal vein tumor thrombus (78.3%), Group 2 (Gr 2) included 196 patients with a subdiaphragmatic IVC tumor thrombus (16.4%), and Group 3 (Gr 3) included 63 patients with a supradiaphragmatic IVC tumor thrombus (5.3%). Median survival was 52 mo for Gr 1, 25.8 mo for Gr 2, and 18 mo for Gr 3. In univariate analysis, Gr 1 had a significantly better overall survival than Gr 2 (p<0.001) and Gr 3 (p<or=0.001). No significant difference in survival was noted between Gr 2 and Gr 3 (p=0.613). Prognostic factors for overall survival in univariate analysis were clinical symptoms (p<0.001), tumor size (p<0.001), perinephric fat invasion (p<0.001), Fuhrman grade (p<0.001), histological type (p=0.021), lymph node invasion (p<0.001), and distant metastasis (p<0.001). Independent prognostic factors in multivariate analysis were tumor size (p=0.013), perinephric fat invasion (p=0.003), lymph node invasion (p<0.001), distant metastasis (p<0.001), and IVC invasion (p=0.008). CONCLUSIONS The level of tumor thrombus in the IVC does not significantly affect long-term overall survival in patients with renal cell carcinoma. The overall survival was statistically different for patients with a tumor thrombus in the RV compared to those with IVC involvement. This has to be considered for the next revision of the TNM system, and the pT3b and pT3c stages have to be redesigned.