The present invention relates to a joint prosthesis, comprising two prosthesis members (2, 3) which are adapted to be positioned at different bones (39, 41, 42) at a joint (38), wherein each prosthesis member (2, 3) includes a first and a second screw-like member (4, 5) respectively, which are adapted to be screwed onto the respective bone (39, 41, 42). One prosthesis member (2) includes a member (6) having a socket and the other prosthesis member (3) a member (7) having a head, whereby the socket member (6) has a mounting pin (22) which is insertable into a first hole (10) in the first screw-like member (4) for positioning or locating the socket member (6) thereto and whereby the head member (7) has a mounting pin (27) which is insertable into a first hole (11) in the second screw-like member (5) for positioning or locating said head member (7) thereto. In the first as well as in the second screw-like member (4, 5) there is provided at least one inner second hole (30 and 33 respectively) which is designed to permit insertion thereinto of a rod (31) of a screw tool (32) in order to secure by screwing the first and second screw-like member (4, 5) respectively, at the respective bone (39, 41, 42). The second hole (30 and 33 respectively) is provided in a bottom (17 and 19 respectively) of the first hole (10 and 11 respectively).