An arrangement of a side door on a body of a motor vehicle is provided. The side door is held on the body in a closed position that closes a door opening corresponding to the side door with respect to the transverse direction of the vehicle with at least regional overlapping with a side sill of the body. The side door has a reinforcing element, with which the side door can be supported on the side sill in the event of an application of force, caused by an accident, acting on the side door from the outside in at least substantially in the transverse direction of the vehicle.