Aspects of the invention pertain to a device and method for adjusting the mounting position of the window lifter guide rail of a motor vehicle window, particularly in a frameless motor vehicle door. The device comprises a lower member and an upper member, and a screw that extends through the locking member. The screw is in engagement with a nut that may be rotated to provide adjustment in a first direction. The upper and lower members may also be moved relative to one another to provide adjustment in another direction.