In order to define the indications for spinal fusion in patients undergoing decompression for lumbar spinal stenosis, 114 patients surgically treated were reviewed. Follow-up was 24 to 108 months. Patients were grouped into four categories: 15 with lateral recess stenosis, 45 with central-mixed stenosis, 43 with stenosis following prior lumbar surgery(s), and 11 with scoliosis and spinal stenosis. Only two patients with lateral recess stenosis underwent fusion with fair results. Approximately one-third of those with central-mixed stenosis required a fusion. Results were good in 70%. In those with stenosis following prior lumbar surgeries, although not statistically significant, those who had concomitant decompression and arthrodesis had a better outcome than those in whom decompression only was done. Patients with scoliosis and stenosis had decompression for significant motor and reflex deficits and fusion over the length of their major curves. Patients having decompression for lumbar stenosis with degenerative spondylolisthesis, isolated disc resorption with degenerative facet joints, intervertebral disc disease with instability, and those with scoliosis with multidirectional instabilities benefit from concomitant spinal fusion.