An operation dealing with prolapse of the nucleus pulposus in the thoraco-lumbar region in dachshunds was analyzed. A dorsolateral fenestration with our own modifications was applied in all the animals. The invertebral space was determined on the basis of clinical and x-rays examinations. Seventy percent of the operated dogs responded favourably to the treatment. The time between the first observable symptoms and treatment was instrumental in predicting the outcome of the operation. In all negative outcomes this time exceeded 20 days.