The invention relates to a fastening system for add-on parts on vehicles that allows add-on parts (5) on vehicles (1) to be easily installed and removed. The invention further relates to a vehicle (1) provided with such a fastening system. The fastening system comprises a connection part (2), which lies against the vehicle (1), and a base (3), which is connected to the add-on part (5). The connection part (2) is designed as a profiled element, the outer surface (2h) of the exterior of which corresponds at least in some sections to the outer surface of a prism having the base of a regular polygon having at least one interior angle deviating from 90°. The base (3) comprises a trapezoidal groove (3a) having leg surfaces (3d, 3e) that are arranged at an angle from each other and that are connected to each other by a base surface (3f). The two leg surfaces (3d, 3e) lie flush against two lateral surfaces (2d, 2e) of the connection part (2) that are not directly adjacent to each other. A hole (3b) extends through the base (3) symmetrically with respect to the groove (3a) and centrally through the base surface (3f). The connection part (2) has a receptacle (2g), in which a connecting element (4) engages, wherein said connecting element is inserted through an opening (3b) in the base (3).