The invention concerns a shoulder prosthesis assembly comprising a meta-glenoid element (7) formed by a plate (13) provided with a central tubular block (14) an anchoring members in the glenoid cavity (3), and a glenoid sphere (9) designed to top the metaglenoid element and provided with an axial screw (35) screwed into said pin; the glenoid sphere has an articulated surface (11) designed to co-operate with a cup of an associated humeral prosthesis (2); said assembly comprises means (16, 45, 46; 51, 50, 49) guiding the glenoid sphere adapted to facilitate its being fixed on the meta-glenoid element; said means comprise a pin (46) adapted to be slotted into the tubular block (14) and into an axial passage of the screw (35); the glenoid sphere (9) is thus guided by being slid on the pin (46) until the screw (35) is inserted precisely into the axis of the tubular block (14), wherein it can be screwed without any risk of damaging the thread on the screw and the internal thread of the block. Advantageously, the free end (48) of the screw (35) can likewise be bevelled to facilitate its being inserted in the block (14) without damaging the threads. The inventive arrangement is particular useful considering the difficulties encountered by the surgeon for correctly positioning the glenoid sphere (9) relative to the meta-glenoid element (7) owing to lack of visibility.