An ankle prosthesis, comprising a tibial element and an talar element (30), each provided with anchoring means on the lower extremity of a tibia and on the astragalus, respectively, and each delimiting an articular surface, both articular surfaces being shaped in order to interact as a whole and to provide a relative movement between the two tibial and talar elements around at last one axis. It is especially characterized by the fact that, taking as reference direction the direction of the axis of the tibia on which it is intended to anchor the tibial element, seen in projection on a plane approximately perpendicular to this reference direction, the articular surfaces are curved with a concavity towards the inside of the foot onto which is to be anchored the talar element.