Two cases of intradural herniated lumbar disc in the space L4-L5 are reported and some considerations about this unusual occurrence are made. Sudden onset after physical strength with lumbar pain irradiated to the legs, bilateral reduction of the muscle power for extension movements, bilateral abolition of the ankle jerk reflexes, bilateral Lasègue sign and sensibility disturbances were observed in both patients. In both cases the protein content of the spinal fluid was elevated and the myelography showed a complete block between L4-L5. Both patients were submited to lumbar laminectomy, a irregular mass between the cauda equina nerves with the aspect of pulpous nucleus being disclosed and completely removed. The postoperative course was uneventfull with complete recovery.