A clinical case of a clear-cells renal tumour, located in the left kidney, with occupation of renal vein by a 7.7 cm thick tumoral thrombus, not affecting the cava vein lumen is presented. CAT and selective left renal venography were the exploratory means which provided the diagnosis. In the study of renal vein affectation by tumoral thrombus, the CAT accuracy can be equal to that of venography, the latter being indicated in dubious cases.