An endoprosthesis used to replace an ankle joint, comprising a lower component (4) which is joined to the ankle bone (2), an upper component (3) which is joined to the shinbone (1) and an intermediate part (5) which forms a slip joint with the lower and upper components. An intermediate part (5), whose sagittal section is wedge-shaped, is provided in order to compensate for anatomical or operative irregulararities. The frontal or sagittal section of the upper component (3) can also be wedge shaped.