To assess the diagnostic accuracy of CT scanning in lumbar stenosis, twenty-nine patients in whom water-soluble myelography showed degenerative bony encroachment of suggested developmental narrowing of the spinal canal were scanned at all lumbar levels, and CT images were compared with myelographic findings. In developmental stenosis computerised tomography was found to be less accurate than water-soluble myelography, whereas in most cases of degenerative stenosis CT findings correlated well with myelographic patterns. An intermediate accuracy index was found in combined stenosis. In central degenerative encroachment of the spinal canal surgical treatment may be undertaken on the basis of CT findings. In the preoperative evaluation of the other types of lumbar stenosis CT scanning with 8-mm thick slices represents a useful adjunct to myelography, but cannot replace this investigation.