The invention relates to an hydraulic unit for a motor vehicle brake system which operates according to the feedback principle, for which purpose a low-pressure accumulator is provided between the outlet valves of the wheel brakes and a pump, and the piston of which low-pressure accumulator, in the basic position, disconnects the hydraulic connection between a pressure medium chamber and a connection leading to the pump such that, in the empty state of the low-pressure accumulator, the wheel brakes are reliably disconnected from the suction side of the pump.