The Patient-Specific Index is used to assess the outcome of total hip arthroplasty by evaluating the preferences of the individual patient. The purpose of this study was to determine the reliability, validity, and responsiveness of this index and to compare different methods of combining patients' ratings of the severity and importance of their complaints, to obtain Patient-Specific Index summary scores. All patients who were scheduled to have a total hip arthroplasty performed by one surgeon at a single institution were eligible for the study. The patients completed the Harris hip score form, the McMaster-Toronto Arthritis (MACTAR) Patient Preference Disability Questionnaire, the Short Form-36, the Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and the Patient-Specific Index. With use of the Patient-Specific Index, patients rated the severity and importance of each complaint. These ratings were summed in four different ways to derive severity-importance scores. The questionnaires were completed twice (two weeks apart) before the total hip arthroplasty and twice (two weeks apart) six months after the total hip arthroplasty by a subset of the patients. The seventy-eight participating patients had a mean age of 62.2 years (range, twenty-five to eighty-seven years) at the time of the operation. Forty-three patients (55 per cent) were men, and sixty-three (81 per cent) had osteoarthrosis. The inter-rater and intra-rater test-retest random-effects intraclass correlation coefficients of the Patient-Specific Index were 0.77 or greater (greater than 0.75 is considered excellent). Construct validity was shown by correlations of the Patient-Specific Index with other scales. The additive versions of the Patient-Specific Index (with a responsiveness statistic of 3.3 or greater and a standardized response mean of 1.6 or greater) were more responsive than the other scales. We concluded that the Patient-Specific Index is reliable, valid, and responsive. The additive versions were the most responsive and are recommended for future applications. Such indices need to be tested in studies of patients who have osteoarthrosis of the hip and other musculoskeletal diseases, to ensure generalizability of the results.