With the advent of computed tomography of the lumbar spine, the theories of a small number of pioneering physicians regarding the pathologic sequela of degenerative disc disease and the entities of central and lateral spinal stenosis have been translated into objective determinations which can now be observed by all. CT scanning has provided clinicians with a better appreciation of the diagnostic limitations of myelography and of the pathologic sequela of hemilaminectomy, dorsal-lateral fusion, and discectomy itself. Since the identification by CT scanning of the loss of disc volume, leading to lateral nerve entrapment and nerve compression resulting from fusion overgrowth, it has become clear that our present modes of therapy require comprehensive reevaluation. Because of the findings of CT scanning, dorsal-lateral fusion now appears to have a much reduced role in the treatment of degenerative disc disease and spinal stenosis. In an era in which unnecessary surgery is a matter of concern, CT scanning is an important means of ensuring that surgery will be undertaken only after thorough analysis of the patient's condition and that surgery will not induce additional pathologic conditions.