The higher prevalence of venous disorders in the left lower limb is currently ascribed to compression of the left common iliac vein (LCIV) by the right common iliac artery (RCIA). This study evaluated the occurrence of LCIV compression by the left common iliac artery (LCIA).The anatomy of iliac vessels was evaluated by computed tomography (CT) in 100 asymptomatic individuals. Traditional axial projections, multiple planar, and curved planar reconstructions were used to investigate LCIV morphology.Compression of the LCIV by the LCIA was found in 20% of participants, whereas compression by the RCIA occurred in 25% and by both iliac arteries in 21%. Axial projections demonstrated a mean reduction in caliber of the LCIV at LCIA crossing of 22.25% (range 0%-90%). Caliber reduction of >20%, 50%, and 70% was observed in 41, 21, and 6 individuals, respectively. The mean LCIV reduction in caliber at RCIA crossing calculated in the axial CT was 24.49% (range, 0%-95%). Caliber reduction of >20%, 50%, and 70%, was observed in 46, 22, and 5 subjects, respectively. Multiple planar reconstructions demonstrated that in contrast to the RCIA, the compressive LCIA determines an eccentric deformation of the vein along its major axis, thus inducing a marked distortion of the lumen that varies from 22 to 37 mm.LCIV compression by the LCIA occurs in a relevant number of asymptomatic individuals and compression by the RCIA coexists in about one-half. The patterns of compression by LCIA correlate well with venographic and anatomic findings, which demonstrated damage of the LCIV unrelated to the RCIA crossing. Further investigations are needed to evaluate the hemodynamic and pathophysiologic implications of such compressive relationships. In fact, even if not necessarily associated with chronic venous disorders, LCIV compression by the overlying arteries must be considered a condition "permissive" of future development of chronic congestion or iliofemoral thrombosis.