The Norwegian Orthopaedic Association established The Norwegian Arthroplasty Register in 1987, first as a hip prosthesis register, but from January 1994 it was extended to include all artificial joints. The main aim has been to survey the results of joint replacement surgery. The orthopaedic surgeons in all hospitals in the country of Norway have agreed to participate. More than 60,000 total hip replacements have been registered so far. Both primary operations and revisions are reported, and by using the patients' national identification numbers, we can link the revisions to the primary operation and perform survival analysis of the implants, with adjustment for potential confounding by factors such as age, gender, and diagnosis. As the prosthesis components are registered on an individual basis, survival of components such as the cup or the stem can be calculated separately, with revision used as an end-point. The reason for revision is registered, and we can assess the rate of revision due to aseptic loosening of the stem or cup, infection, dislocation, wear, osteolysis, or other reasons. For the safety of the surgeons, and to obtain a complete reporting of failures, we do not register the name of the surgeons and we keep the individual hospitals' results confidential. The operating costs of register are covered by the state and the register is not dependent on grants from the industry. The cost per registered implant is approximately $18 (US). With this system we have been able to detect inferior results of implants as early as after three years of use. Several brands of uncemented prostheses and two brands of cement have been withdrawn from the market mainly based on our findings.