This report is made to record the occurrence of an extruded disk migrating to the dorsal extradural space at the level of L3-L4. In a recent survey of the literature, Rubinstein, Stern, and Jacobson (2) reviewed the subject of blocking of the spinal canal, complete and incomplete, by extruded disks. In no instance was the entire nucleus pulposus found dorsal to the thecal sac. Case Report A 39-year-old-male was seen nine days after experiencing a sudden pain in the left calf, upon getting out of bed in the morning. This was so severe that the patient was immediately incapacitated; it subsequently spread to the right buttock and was accompanied by weakness of both legs which soon progressed to complete inability to walk. Two days prior to hospital admission bladder and bowel function failed. The patient was an extremely obese, heavily built man, apparently suffering intense discomfort, with abdominal distention and urinary retention. There was tenderness on deep pressure over the mid-lumbar area, and the slightest motion caused severe exacerbation of pain. The lumbar curvature was flattened and there was spasm of the paravertebral muscles bilaterally. Motor examination demonstrated an almost complete paralysis of the feet, with retention only of very minimal plantar flexion. There was a 50 percent loss of extension of both knees and about 25 percent loss of flexion. The hips showed 75 per cent loss of external rotation and abduction, as well as weakness of internal rotation and adduction. Flexion of the hips was minimal. Deep tendon reflexes were completely absent in both lower extremities. Sensory examination showed a complete loss of pain sensation from L4 downward on the left and from Sl downward on the right. This included involvement of the saddle area. Position sense, touch, and vibratory sense were also absent distally in the left lower extremity but were partially intact distally in the right lower extremity. Plantar responses were inactive. The abdominal reflexes were intact. Straight leg raising was limited bilaterally to 45°. On catheterization 1,000 c.c. of residual urine was obtained. Plain roentgenograms of the lumbar spine showed a transitional vertebra at the lumbosacral junction(sacralization of the fifth lumbar vertebra), with minimal exostosis formation about the lower lumbarvertebrae. There was slight thinning of the intervertebral disk cartilage at the levels of L4-L5 and L5-S1. A lumbar myelogram demonstrated a complete block to the passage of the contrast agent caudad, just above the level of the L3-L4 interspace (Figs. 1–3). A lumbar laminectomy was performed as an emergency procedure and, after removal of the lamina of L3 and L4, an extradural mass was identified. This was first thought to be a tumor but, following dissection from the dura, a thin strand of attachment was followed laterally around the left side of the spinal canal and was seen to enter the interspace at the L3-L4 level.