 An important drawback of all INPH studies so far is the rather limited number of patients and, the mixing of idiopathic NPH patients primary NPH with those of known cause secondary NPH such as trauma, subarachnoid hemorrhage and stroke.INPH is considered a multfactorial condition with a disturbance of CSF circulation as well as parenchymal abnormalities in a vulnerable population with much comorbidity. Because of the many outcome variables a study on the prediction of outcome needs large numbers of INPH patients. With a few exceptions, previous studies on CSF dynamics in INPH were conducted in single high quality institutions. We also have to demonstrate that the same or even better results can be obtained with international cooperation providing higher patients numbers. Therefore we intend to conduct a large European multicentre study on INPH including at least 200 patients. All these patients will receive the same shunt system and will be followed-up by a standardized protocol using primary and secondary NPH outcome measures. Because of the continuing controversy with respect to the appropriate shunt opening pressure and the many problems of over- and underdrainage after insertion of the shunt, we chose the Codman Hakim programmable valve 8. 