A motor vehicle door having a frame defining a window opening, and a window lift system having a first guide rail, a first sliding piece guided on the first guide rail, a second guide rail, a second sliding piece guided on the second guide rail, a cable drum and a drive cable driven by the cable drum and coupled to the sliding pieces, the drive cable guided in a Bowden cable sheath between an upper end region of the second guide rail and a connection region located between an upper end region of the first guide rail and a lower end region of the first guide rail. The Bowden cable sheath fastened in the upper end region of the second guide rail and in the connection region of the first guide rail.