With the advent of CT we entered a new area of radiological imaging. Structures which rarely if ever were seen became apparent. In no part of the body was the impact of CT as profound as it was in the retroperitoneum. In the pre-CT area this region of the body could not be directly studied and only when gross abnormalities were present could they be appreciated. The best we could do was to try to identify a suspected process by studying its effect on surrounding organs whose position might have been affected by the growth. Urography, barium studies or angiography were employed in the hope that variation in the position of the vessels, ureter or bowel would lead us to the correct diagnosis. With computed tomography all this changed. Modern scanners, available to all today, permit us to appreciate details undreamed of only few years ago. The abundance of fat in this region helps to clearly show even the smallest of structures. We now have the ability to recognize small vessels, lymph nodes and fascial planes. We had a tool which permitted us to study structures which hitherto were only seen by the anatomist or during surgical dissection.