An electronically slip-controllable power-assisted braking system for a motor vehicle. The power-assisted braking system is equipped with a hydraulically acting booster device that is inserted in a brake circuit downstream from an actuation device and has a piston unit movably guided in a cylinder housing. The piston unit is embodied in stepped fashion and divides an interior space of the cylinder housing into multiple booster chambers impinged upon by pressure medium. At least one of these booster chambers is capable of being impinged upon by pump pressure from a pump driven by external force.