A pump unit for a hydraulic vehicle brake system with traction control has an electric motor driving a radial piston pump. A rotor shaft of the pump unit has a hollow shaft with two standardized, hardened cylindrical pins that are press-fitted into the ends of the hollow shaft. The rotor shaft can be produced simply, economically, and without metal-cutting machining. The hollow shaft has high bending and torsional strength. The rotor shaft has a small diameter at the bearing points, which makes a small bearing diameter and thus a small installation space for the pump unit possible.