Both circumaortic and retroaortic left renal veins are the result of persistence of the dorsal limb of the embryonic left renal vein and of the dorsal arch of the renal collar. However, in retroaortic left renal vein the ventral arch regresses so that a single renal vein passes posterior to the aorta. The approximate prevalence of circumaortic left renal vein is 0.3 to 3.7%, and retroaortic left renal vein is 0.5 to 6.8%. Cross-sectional computerized tomography study was done in both cases. In one of the cases the left renal vein was observed posterior to the abdominal aorta and in the other case the left renal vein was covering the abdominal aorta, one vein superior and posterior and the second vein inferior and anterior to the abdominal aorta. Venous anomalies of the renal veins are clinically important especially in retroperitoneal surgery and intracaval interventions. These anomalies should not be misdiagnosed as dilated gonadal vein, retroperitoneal lymphadenopathies or masses.