The several theories on the pathogenesis of syringomyelia have not resulted in the satisfactory selection of those patients who can be treated by CSF diversion.In the present paper three types of syringomyelia are described by case studies. The classification is made by investigation of CSF-dynamics, a measurement of CSF pressure and resistance to outflow of CSF. It is proposed that in a subgroup of patients with syringomyelia the cause is defective CSF resorption and that this group may be selected out and treated accordingly.