Abstract: A method and tool for inserting a prosthetic stem component in an aligned position into a prepared bone cavity. The bone is prepared by removing bone material from the bone canal and preferably also machining an entry opening of a predetermined shape and desired orientation in the bone, or marking the plane of the joint on the bone end. The tool includes an upper component that engages the top of the prosthesis stem to fix its rotational alignment, and an arm that extends to the opening in the bone and is aligned at its distal end. The upper component rides along the arm, and orients the stem with respect to the bone as the stem is inserted. The tool may include a lower element that engages the machined or marked bone and holds the arm to orient the head of the prosthesis. Optionally, the lower element may guide the distal stem. Alternatively, the guide may include an arm that simply points to, contacts or fastens at the bone end, orienting the prosthesis insertion without sighting errors.