A spindle gear unit (10), for an adjusting mechanism in a motor vehicle seat, includes a housing (20, 22), a spindle nut (40, 140, 240) cooperating with a spindle (30). The spindle nut (40, 140, 240) has external toothing (44, 144, 244) and has at least one bearing surface (46, 146, 246) for rotatably mounting the spindle nut (40, 140, 240) in the housing (20, 22). A thrust washer (50, 150, 250) is put on and encompasses the bearing surface (46, 146, 246). A screw (70) is rotatably mounted in the housing (20, 22) and has a worm gear (72) which is in engagement with the external toothing (44, 144, 244). The thrust washer (50, 150, 250) is pressed onto the spindle nut (40, 140, 240). A vehicle seat is also provided with the spindle gear unit for driving a seat rail of a length adjuster of the vehicle seat.