The anatomy of 54 pairs of lumbosacral nerve roots was described in nine fresh adult cadaver specimens, with particular attention given to the fixation of the nerve roots to surrounding skeletal and ligamentous structures in the lumbar spine. Dural ligaments were identified fixing the dura and nerve roots at their exit from the main dural sac to the posterior longitudinal ligament and vertebral body periosteum proximal to the intervertebral disc. Distal fixation occurs at the intervertebral foramen where the epineural sheath of the spinal nerve is attached. The overall arrangement is one which tends to hold the exiting nerve root anteriorly in the spinal canal. Mechanical analysis of this anatomical arrangement explains how pressure can be applied to the extrathecal nerve root by a disc protrusion without compression of the nerve root against the posterior elements. The possible role of the dural ligaments in the pathogenesis of the sciatica syndrome is discussed.