In 842 patients, with the clinical diagnosis of root compression due to a disc herniation, laminectomy failed to reveal any lesion of the intervertebral disc in sixty-eight patients. In nine, the source of the root compression was found to be foraminal migration of a sequestrated portion of the intervertebral disc; in twelve, pedicular kinking; in nineteen, articular-process impingement; in eight, segmental spinal stenosis; and in two, a lateral disc protrusion. In eighteen explorations, performed early in the series, no cause could be found for the root compression, and it is suggested that the lack of findings in these cases was due to inadequate exploration of the nerve root. The series analyzed is too small to make any dogmatic statements. However, a plea is entered for a careful appraisal of the level of root involvement preoperatively, using all ancillary methods available—myelography, discography root-sleeve injection, electromyography, diagnostic differential epidural injections—in patients without objective signs of the site of root involvement. Armed with such evidence, it is suggested that a radical exposure of the nerve root should be undertaken in all patients in whom the intervertebral disc fails to reveal pathological changes of sufficient degree to account for the nerve-root compression or tautness demonstrated.