Abstract: A thumb prosthesis includes a trapezial component adapted to be fixed in the trapezium and a metacarpal component adapted to be fixed in the metacarpal bone. The trapezial component has a self-cutting thread adapted to be screwed into the trapezium; a polygonal base, having a conical surface and a neck part and being situated at one end of the self-cutting thread; and a spherical head disposed on the conical surface and extending from the neck part. The metacarpal component has a frustoconical head having a large-diameter end and an opposite, small-diameter end and a geometrical axis; a hemispherical socket provided in the small-diameter end and receiving a surface portion of the spherical head; and a stem extending from the large-diameter end of the frustoconical head. The stem is offset relative to the geometrical axis and has a decreasing triangular cross section with rounded corners as viewed in a direction away from the frustoconical head.