A window shade for motor vehicles having a shade of approximately trapezoidal shape. An extension profile or pull rod of the shade, the ends of which are guided in guide rails, is arranged on the shortest transverse edge of the shade. In order to compensate for a varying distance between the guide rails, the extension profile is divided into a center section, on which the shade is fixed, and two end sections that move in the guide rails. Centering devices are provided in order to prevent transverse creases in the shade when it is completely extended. The centering devices, which are effective when the shade is completely extended, act upon the center section.