This study investigated the collateral flow emanating from and around the renal veins in the adult. Experimental venous occlusion was performed along several venous pathways under the influence of the renal veins. Radiological techniques were used to investigate renal venous collateral flow. The importance and contribution of these collaterals are discussed with reference to their diagnostic, therapeutic, and prognostic implications. The left renal vein is a major venous collateral pathway, whereas the right renal vein contributes little.