1. Nine patients with radiological evidence of narrowing of the lumbar spinal canal, proved at operation, are reviewed.

2. They presented with either a claudicant or a sciatic clinical picture.

3. A classification into primary or secondary spinal stenosis is described. The primary type may be due to a reduction in either the sagittal, coronal or both diameters of the spinal canal.

4. Secondary narrowing of the canal may be superimposed upon a primary anatomical abnormality or may cause narrowing in a previously normal canal.

5. The symptoms are thought to be caused by a further reduction in the size of an already narrow canal, producing traction on the nerve tissue, which is then unable to move freely.