The Swedish National Total Hip Arthroplasty Register contains more than 200,000 primary and secondary hip replacements. The failure end-point definition is revision. The aim of this thesis was to validate the results presented by the register and to study the outcome of hip replacement surgery in Sweden. The hypothesis was firstly that the number of failure reported to the Swedish THA register are valid and secondly that adding clinical and radiographic failure criteria will dramatically decrease the survival rate for THR implants. The study consisted of three parts with 2-10 years follow-up of patients with total hip replacements (THR). In part I, three general health questionnaires (Nottingham Health Profile, SF-36, EuroQol) and two disease-specific instruments (WOMAC, Harris Hip Score) were tested for validity and reliability (n = 62). The results showed the disease specific questionnaires are at least as valid and reliable as the general instruments are. In part II, all THRs reported to the Swedish THA register 1986 to 1994 (84,884 primary and 10,176 revision hip replacements) were compared with the data from the Discharge register and the Cause of Death register in Sweden. 2,604 patients were randomly selected from the Discharge register to determine if they had undergone any revision surgery. The study showed that the Swedish THA register covers 94% of the revisions actually performed in Sweden and the results did not differ significantly from the data in the Discharge register and the results reported by the patients. In part III, 1,056 patients from the selected cohort were studied further concerning general health and disease-specific health, using the Nottingham Health Profile, SF-36 and WOMAC. An age and gender matched subcohort of 344 patients were then examined clinically, using the Harris Hip Score, and radiographically. The clinical and radiographic failure rates were in several tests as high as the revision rates documented in the Swedish THA register. The clinical results were, however, dependent on demographics, the definition of clinical failure and the scoring system used. The results presented by the register with revision as failure end-point give an exact but limited information about the quality of hip replacement surgery in Sweden.