Abstract: An apparatus for treating hydrocephaly has one housing which contains subcutaneously immplantable components for the measuring and controlling of fluid pressure. A second housing adapted to cooperate with the components in the first mentioned housing, contains the measuring and control components which remain outside a patient's skin. The components in both housings and the housings themselves are arranged for cooperation with each other, whereby an intracerebral space may be automatically drained in response to a predetermined, adjustable pressure.