Four patients in whom the S-ROM Total Hip System Polydial polyethylene liner was used illustrate the importance of, and difficulties in, detecting polyethylene wear-through before a complete acetabular revision is necessary. The patients in these cases had full thickness polyethylene wear-through 11 or more years after total hip arthroplasties. Dorr and Livermore wear measurements from radiographs of the patients underestimated the actual wear and did not indicate wear-through. Because excessive head penetration was not evident radiographically with the S-ROM components, the cases showed the necessity of using additional measures to diagnose wear-through, particularly with these components. Repeat radiographs at a higher kilovoltage were used to better visualize the outline of the femoral head, and hip aspiration was used to diagnose metallosis. These cases also showed the importance of yearly followup evaluations, especially 10 or more years after surgery for patients with the S-ROM Polydial locking mechanism.