Twenty two of fifty five patients initially suspected of suffering from normotensive hydrocephalus were surgically treated (CSF ventriculoatrial shunt). The results of surgery were related to the findings of the different diagnostic examinations (pneumoencephalography, isotope cisternography, transfer fron CSF to blood of isotope labelled serum albumin, constant infusion manometric test, long lasting intraventricular pressure recording). 1.Pneumoencephalography, intraventricular pressure recording, and, above all, isotope cisternography provided the most reliable data for diagnosis and surgical prognosis. 2. The combined use of pneumoencephalography and isotope cisternography was sufficient for a correct diagnosis and surgical prognosis in about 50% of the patients examined. 3. When the diagnostic information given by the combined results of the two above examinations was not sufficient, intraventricular pressure recording proved to be the most useful examination to supplement it. 4. The relation of the results of the study of transfer of istope labelled serum albumin from CSF to blood and of the constant infusion manometric test to the surgical outcome was uncertain.