A prospective, national multi-center study of all reoperations after total hip replacement (THR) was started by the Swedish Orthopedic Association in 1979. The material comprises all THR performed in Sweden, presently more than 10,000 yearly or 130 THR per 100,000 inhabitants; uncemented implants have been used in less than 2 percent. The main reasons for revision have been aseptic loosening 79 percent, infection 10 percent, technical error 6 percent, and dislocation 2 percent. The cumulative rate of revision for deep infection has dropped from 0.9 percent to < 0.5 percent for implants inserted 1979 and 1983, respectively. With the Charnley prosthesis as the gold, standard the performance of other prostheses was analyzed. Improved cementation techniques and anti-infection measures have continuously reduced the revision risk. The register demonstrates that the average orthopedic surgeon cannot match the results achieved by experts. However, the vast majority of THR, worldwide, are not performed by experts. Quality-assurance in this sector of orthopedics demands a continuous analysis of the outcome of these operations.