Four cases of vascular complications to anterior perforations during discectomy prompted a CT study to measure lumbar disc diameters and to evaluate the prevertebral anatomy. Fifty young adults who had been referred for low-back pain and/or sciatica but had not undergone operation were included. In five additional patients, prone versus supine CT examinations were compared. Six typical configurations of the vascular anatomy could be classified to explain the type of vascular complications occurring at the L3-4 and L4-L5 disc levels. The sagittal diameter of the three lowest lumbar discs varied from 33 to 56 mm, indicating the importance of this parameter as an intraoperative guideline for the spine surgeon. Air-filled intestines were observed anterior to the L5-S1 disc predominantly in the prone position. The possible relationship between this finding and postoperative discitis is discussed.