A rear wing for a motor vehicle has a wing roof and a wing bottom formed as a hollow body. A reinforcing structure is arranged inside the hollow body and has several upright webs, of which at least one cross web extending in a transverse direction of the vehicle is connected with the interior surface of the wing bottom. At least one drainage opening is provided in the wing bottom. In order to be able to drain water penetrating into the hollow body, the at least one cross web has a plane web surface which forms a wall of a water channel, and the at least one opening is arranged in the course of the water channel.