A trial system for a prosthesis is described. The prosthesis can include an acetabular prosthesis generally for implantation in an acetabulum and the surrounding pelvis. The acetabular prosthesis includes an acetabular cup having a substantially concave inner surface and a substantially convex outer surface. One trial shell or a collection of trial shells are provided to trial a range of motion of the hip joint before implanting a shell prosthesis into the acetabular prosthesis.