Trailer coupling for motor vehicles

The trailer coupling (1) for motor vehicles has a ball arm (3) pivotably and axially movably mounted on the vehicle and with a coupling ball (2) on its free end. A seal is fitted between the ball arm bearing head (4) and attachment flange (5) lying opposite and is pretensioned against the flange in any operating position of the ball arm bearing head. The inside diameter of the seal is smaller than the outside diameter of an encompassing shoulder provided on the ball arm bearing head for the slipping on of the seal.