Forty embalmed cadavers (24 men and 16 women) were obtained to evaluate the anatomic features of iliac vessels with respect to the anterior approach to the lumbosacral junction. Through a midline longitudinal incision over the linea aspera and retraction of the intraperitoneal contents, exposure of the abdominal aorta, inferior vena cava, and common iliac vessels was done. Direct measurements regarding the relations of these greater vessels to the sacral promontory were then performed. The results showed the average width of the trigone, measured between the medial edges of the left common iliac vein and the right common iliac artery, was 55.9 mm for male and 55.3 mm for female subjects, respectively. The average height of the trigone, measured from its apex to the sacral promontory, was 36.9 mm for male and 35.2 mm for female subjects separately. The width of the uncovered left common iliac vein averaged 7.2 mm for male and 6.3 mm for female subjects, respectively, with a range of 3-11 mm for both male and female specimens. One should be always aware of the medially placed left common iliac vein and an approach medial to the right common iliac artery to the L5-S1 disk is recommended if anterior surgery is desired.