Among giant tumours of the cauda equina, apart from ependymomas, neurinomas merit a special place. Depending on their site, they give rise to severe lumbar pain or root pain, with, almost constantly, aggravation during the night. X ray suggests the diagnosis when one finds displacement of the bone without inflammation, a regular bony defect, well-limited and asymmetric, and when the tumour is frequently prolonges in several directions across the bony orifices, sometimes giving a very large paravertebral mass which requires a double approach during surgery. The prognosis of isolated neurinomas is excellent, with disappearance of the pain immediately after operation, regression of the neurological signs or, at any rate, stabilisation when the latter are important. As far as the problem of spinal stability is concerned, this has been solved by sufficient spontaneous bony reconstruction.