An instrument (102) for positioning a cup component (104) of an orthopaedic joint prosthesis is described. The instrument includes an actuator (124) and a plurality of jaw members (152, 154, 156, 158) around a longitudinal axis. Each jaw member includes a mounting end (162), a gripping end (166) and a surface (174) between them. The gripping end has a transversely extending member (168) which can be received in a recess in a wall of a cup component and can displaced between a retracted position and a deployed position. The surface is inclined to the longitudinal axis of the instrument and curved in an outward direction away from the longitudinal axis. The actuator and the plurality of jaw members are capable of relative movement along the longitudinal axis of the instrument with the actuator in contact with the inclined surfaces of the jaw members so that said relative movement causes the jaw members to move between their retracted position and deployed position.
