The physiopathological conditions of the normal pressure hydrocephalus syndrome are analysed. Within a group of 21 patients with clinical sinto- mathology pertaining this entity, only were 10 selected with a clinical, radiological and cisternografic indubitable diagnosis. It has been noticed that in spite of the stricked selection only a 50% of them have been beneficed by the application of a low pressure valve. Then, the hypothesis that the disease is a multicausal syndrome appears, which by an identical physiopathologic process produces or exhibits a similar clinical, radiological and cisternographic picture. Only those patients on whom the mechanical problem is solved would be beneficed by neurosurgery.