Spinal stenosis and degenerative spondylolisthesis share many symptoms and the same treatment, but their causes remain unclear. Bone mineral density has been suggested to play a role. The aim of this study was to investigate differences in spinal bone density between spinal stenosis and degenerative spondylolisthesis patients. 81 patients older than 60 years, who underwent DXA-scanning of their lumbar spine one year after a lumbar spinal fusion procedure, were included. Radiographs were assessed for disc height, vertebral wedging, and osteophytosis. Pain was assessed using the Low Back Pain Rating Scale pain index. T-score of the lumbar spine was significantly lower among degenerative spondylolisthesis patients compared with spinal stenosis patients (-1.52 versus -0.52, P = 0.04). Thirty-nine percent of degenerative spondylolisthesis patients were classified as osteoporotic and further 30% osteopenic compared to only 9% of spinal stenosis patients being osteoporotic and 30% osteopenic (P = 0.01). Pain levels tended to increase with poorer bone status (P = 0.06). Patients treated surgically for symptomatic degenerative spondylolisthesis have much lower bone mass than patients of similar age treated surgically for spinal stenosis. Low BMD might play a role in the development of the degenerative spondylolisthesis, further studies are needed to clarify this.