Spondylolisthesis was observed in 165 of 2,500 patients with back pain evaluated by CT. In more than two-thirds of these patients a second structural abnormality was found in association with the spondylolisthesis. The nature and location of this second abnormality varied with the type of spondylolisthesis: spondylolytic or degenerative. Spondylolytic spondylolisthesis, caused by a defect in the pars interarticularis, was associated with foraminal stenosis at the level of the defect in the pars and disk protrusion at the interspace immediately above this level. Degenerative spondylolisthesis, caused by facet joint disease, was associated with disk protrusion and spinal stenosis at the same level as the spondylolisthesis. The advantages and limitations of CT in the evaluation of symptomatic patients with spondylolisthesis are discussed.