The diagnostic evaluation of patients with previous lumbar surgery presents a problem clinically and radiographically. The authors evaluated radiographically 75 patients with previous lumbar surgery who had persistent lumbar symptomatology. From their series, they found that a combination of two modalities (1) plain radiographs of the lumbar spine and (2) CT with intrathecal metrizamide and/or intravenous contrast provided the most complete and useful diagnostic information. The findings are presented with an emphasis on the pathologic changes demonstrated on the CT scans of the lumbar spine of which the most persistent findings were granulation tissue at the surgical site, lumbosacral spondylosis, recurrent or residual herniated disc, and arachnoiditis.