BACKGROUND: The clinical importance of tumor thrombus in patients with renal cell carcinoma is unknown. We sought to determine the long-term risk of venous thromboembolism (VTE) in patients with residual tumor thrombus postextraction, and to evaluate the impact of residual tumor thrombus on overall survival. PATIENTS/METHODS: A cohort study of patients with stage III-IV renal cell carcinoma undergoing nephrectomy was undertaken. The primary endpoint was the risk of VTE during a 2-year follow-up period. The secondary endpoint was 2-year overall survival. RESULTS: A total of 170 surgical renal cell carcinoma patients were included, 97 (57.1%) of whom had tumor thrombus. Patients with residual tumor thrombus following surgery had a higher risk of developing VTE than those with complete tumor thrombus resection (hazard ratio [HR] 8.7, 95% confidence interval [CI] 1.7-43.4) and no tumor thrombus (HR 6.5, 95% CI 1.7-24.7). Patient with residual tumor thrombus did not have worse overall survival than those with tumor thrombus completely resected or those without tumor thrombus. CONCLUSIONS: The presence of residual tumor thrombus is an important risk factor for VTE among renal cell carcinoma patients.