A ball screw including a threaded spindle and a spindle nut has a ball deflector arranged in an opening in the lateral surface of the spindle nut. The ball deflector is formed with an upper shell and a lower shell, the lower shell being arranged radially inwardly closer to the spindle nut longitudinal axis than the upper shell. The lower shell has a substantially half-shell-shaped contour. Both the upper shell and the lower shell are fastened in the spindle nut without any further, discrete mechanical fastening elements, and the ball deflector formed thereby does not protrude beyond the outer contour defined by the spindle nut.