The authors performed single- or multiple-level unilateral laminectomy to treat lumbar spinal stenosis in patients with mild to moderate leg pain and compared the results with those from patients treated with conservative therapy in a prospective study. This decompression technique produced a 68% rate of improvement compared with a 33% rate for conservatively treated patients. The surgical group exhibited significant and sustained improvement, whereas the functional and clinical status of the conservatively managed group had returned to baseline during the same period. The preoperative dural sac cross-sectional area at the level of the most stenosis was 70.76 +/- 28.2 mm(2) for the surgical group, whereas on postoperative scans it was 108.12 +/- 31.5 mm(2), with an average correction rate of 65%. Neither new degenerative spondylolisthesis nor any evidence of instability was detected in any patient during the study.