The renal vein normally is located in front of the aorta. However may course posterior to the aorta. This variation is of importance during procedures in the retroperitoneal region. The objective of this study was to investigate the incidence of the retro – aortic left renal vein. A total of 13 cadavers and 10 visceral blocks were used for the study in the laboratory of Morphology of the University of Pamplona. In two cadavers, three renal veins were found to bind and give rise to a common venous trunk corresponding to the left renal vein passing behind the aorta abdominal (retro-aortic) and ending at the inferior vena cava at the level of the fourth vertebra lumbar. Knowledge of anomalies of left renal vein is essential for radiologists, endocrinologists, fertility specialists, urologists and surgeons, in determining the feasibility of complication-free surgical interventions