In this report, the author presents a rare case of a 59 year-old man with ILDH. It was the only case of ILDH among 960 patients surgically treated, during the period 1989-1996. Clinically the patient demonstrated an acute cauda equina syndrome. The diagnosis was established by radiculograms, which showed a total block at the L3-L4 level. There was a 3 days time interval between the diagnosed syndrome itself and the operation. At surgery the L3-L4 level was intact, whereas dense adhesions were found between the L4-L5 disc and the dura. Root retraction to expose the nucleus pulposus mass was impossible. A laminectomy of the L4 was undertaken. An incision was made in the dura and arachnoid, revealing an extruded discal mass, lying between the roots of the cauda equina. It was carefully removed. The state of the patient at follow-up 1 year after surgery was unsatisfactory. The patient has moderate flaccid paraparesis, bladder dysfunction improved. The prognosis appeared to be linked to the preoperative duration of symptoms.