The fascial structure of the left retroperitoneal region of the abdomen and its surgical anatomy are reviewed. The findings correlate with those of Tobin and Baumann. The muscular interval between the quadratus lumborum and the psoas muscle is elaborated upon as a useful route for entrance into the retroperitoneum. The occasional but significant occurrence of the artery of Haller is mentioned. The author's recommendation for exposure of the upper segments of the lumbar spine L1 through L3 is through a posterolateral abdominal incision with resection of the medial half of the twelfth rib (depending on the configuration of the twelfth rib) and oteotomy of the tip of the L1 transverse process as the routes of exposure of the proximal segments of the lumbar spine.