The aim of the study was to conduct an anatomical and clinical study of IVC and its tributaries, and to determine the pathways of collateral venous blood flow to improve the results of surgical treatment of patients with kidney cancer complicated by venous tumor thrombosis. The anatomical examination of the IVC and its tributaries included the results of autopsy of 27 corpses. The clinical part of the study is based on the results of examination and surgical treatment of 147 patients with renal cell carcinoma complicated by venous tumor thrombosis. Tumor of the right kidney was diagnosed in 96 (65.3%) patients, left - in 51 (34.7%) patients. Venous tumor thrombus was localized exclusively in the renal vein (level 0) in 55 (37.4%) cases, while in different IVC segments (levels I-IV) - in 92 (62.6%) cases. At the same time, level I took place in 32 (21.8%), level II - in 30 (20.4%), III - in 22 (15.0%) and IV level - in 8 (5.4%) patients. The spread of a venous tumor thrombus into the main hepatic veins was diagnosed in 1 (0.7%), in the left gonadal vein - in 4 (7.8%), in the left adrenal vein - in 2 (3.9%), into the contralateral renal vein - in 2 (1.4%) cases. Tumor thrombosis of the infrarenal IVC, combined with hemorrhagic thrombosis occurred in 28 (19.0%) patients. Avascular IVC parts were found in the retrohepatic segment under the main hepatic veins with a median length of 13.1 mm and in the infrarenal segment under the right renal vein with a median length of 17.8 mm. 6 basic anatomical structures involved in the formation of the caval venous collector were identified. Despite the broad anatomical possibilities for compensating venous blood flow during IVC occlusion of tumor and hemorrhagic genesis, only surgical treatment can provide a good functional result for venous return through the IVC to the heart. Thrombotic occlusion of the renal and inferior vena cava contributes to the retrograde spread of venous tumor thrombi with the involvement of the vessels in the process, providing a collateral pathway for the outflow of venous blood. To successfully perform thrombectomy from IVC, it is necessary to actively use avascular parts in its retrohepatic and infrarenal segments, taking into account the existing variability in the localization of the posterior and anterior IVC inflows.