An acetabular prosthesis (1) for hip arthroplasty, comprising a metal- back (3) in which a cavity (5) is formed which is adapted to accommodate an insert (7) and which comprises a first region (50) having a substantially hemispherical internal surface (52) from which a second region (54) extends which has a substantially cylindrical internal surface (56), the height of the second region (54) being comprised in the interval between 1 and 5 millimeters and being adapted to help to retain the insert (7) in the cavity (5).
