Abstract: A surgically implantable flow control device positionable over a burr-hole through a patient's skull is provided for use in shunt systems for controlling the release of entrapped body fluids. The device includes a rigid base including an inlet port and a valve seat which surrounds the inlet port, and a flow control member secured to the base. The flow control member has an asymmetric membrane which is resiliently biased to contact the valve seat in a manner forming a releasible seal therebetween, to provide controlled resistance to proximal-to-distal fluid flow through the device. The membrane includes a septum portion overlying the inlet port and a relatively thin portion responsive to fluid pressure differentials on inlet and outlet sides thereof. A membrane shield overlies an outlet side of the membrane and includes a needle guide aperture in alignment with the septum portion of the membrane and the inlet port.