OBJECT: Anterior surgical approaches to the lumbosacral disc spaces are being undertaken with increasing frequency. This increase and the use of minimally invasive techniques themselves have the potential to raise the incidence of major vessel injuries. The purpose of this study was to determine the variability of the vascular anatomy anterior to the lumbosacral spine and to draw conclusions regarding surgical accessibility of the L5-S1 disc space. METHODS: Thirty-five cadavers (age range at the time of death 31-87 years) were obtained to evaluate the anatomical features of iliac vessels with respect to the anterior approach to the lumbosacral spine. Direct measurement and morphological classification regarding the relations of these great vessels to the four arbitrary reference points of the lumbosacral disc space were performed. The mean width and height of the L5-S1 disc were 56.4 mm (range 41.6-65.4 mm) and 18.8 mm (range 10-24 mm), repectively. According to the authors' morphological classification, nine specimens (26%) were found to be Type A (standard), 12 (34%) Type B (narrow), two (6%) Type C (ajar), and 12 (34%) Type D (obstacle). CONCLUSIONS: The authors have noted quite a variation in the venous vascular anatomy anterior to the lumbosacral disc. During surgical planning for the anterior approach to the lumbosacral spine when using any technique, it is vital to assess carefully radiographic and neuroimaging studies to minimize potentially disastrous vascular complications.