Abstract: Disclosed is an acetabular prosthetic cup positioning instrument for use in positioning such cup during total hip surgery. The acetabular cup has a convex outer portion that is disposed in the patient's reamed and prepared acetabulum, the cup has an inner cavity and the cup has a rearward-most portion between such outer portion and inner cavity defining a rim portion. The instrument has an interchangeable ball and flange for respective engagement with such cup's inner cavity and rim portion to mount, orient and align such cup relative to such instrument. A drive mechanism, operatively connected through a drive coupling rod, flexible drive cable and drive member and carrying such ball, effects translatory movement of such ball away from such flange while such ball maintains its engagement with such cup's inner cavity to thereby disengage such flange away from such cup's rim portion.