Abstract: Knee-joint endoprosthesis with a femoral part (10), a tibial part (11), and a bearing element (12) made of plastic, in particular polyethylene, disposed between the femoral and tibial parts, wherein the bearing element (12) is slidably supported on a spherically concave bearing surface (20) of the tibial part (11), which faces the femoral part (10). Above the tibial bearing surface (20) projects a peglike or rodlike stopping device (21), which enters an elongated opening (22) in the supporting and sliding surface (32) of the bearing element (12) that faces the tibial bearing surface (20), in such a way that the bearing element (12) can rotate on the tibial bearing surface (20) and also, to a limited degree, be displaced longitudinally in the plane of knee flexion.