At present, no scientific evidence exists on how to make the diagnosis of lumbar instability; nor is there any proof of successful treatment--conservative or surgical. Judging from available clinical studies, surgical fusion operations may be useful in properly selected patients with spondylolisthesis or in situations for which the surgical approach has necessitated destabilization by laminectomy and facetectomy. Refined biplanar radiographic techniques promise better definitions for future diagnostic studies.