Polyester resin was injected into the epidural space of fresh-adult cadavers to study the shape of the lumbar epidural space and the spatial relationship between the dura mater and vertebral canal. In most of the anatomical preparations the shape of the lumbar dural sac was distinctly triangular and in some cases a dorso-median fold of the dura was apparent. These observations support the explanation suggested by others to account for the midline translucency seen in contrast radiological examination of the lumbar epidural space. Factors which may influence the shape and dimensions of the lumbar epidural space are discussed. It is suggested that these anatomical observations may have clinical significance in the practice of lumbar epidural analgesia.