The retro-aortic left renal vein (RLRV) is a malformation characterized by the presence of a vessel that drains the left renal blood up to the inferior vena cava crossing behind the aortic artery. Varicocele is defined as venous dilation of the pampiniform plexus, and the left side is the most commonly affected. Several theories concerning the possible aetiology of varicocele are reviewed in the literature, but RLRV was not mentioned as an aetiologic factor of varicocele. in this study we investigated the percentage of RLRVs and their relation with varicocele. A total of 1,125 contrast-enhanced abdominal CT scans was examined to identify RLRVs. RLRVs were found in nine women (1.6%) and ten men (1.7%). We performed scrotal Doppler ultrasonography (US) for all affected men except one. Varicocele of varying degrees was found in seven of the nine male patients with RLRV (77%). RLRV could be one of the aetiological factors in the development of varicocele, and the cases with RLRV should be examined by scrotal Doppler US for the presence of varicocele.