OBJECTIVE: To compare the responsiveness of the Functional Assessment System (FAS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Medical Outcomes Study 36-item Short Form (SF-36) in patients with osteoarthritis (OA) scheduled for total hip replacement. METHOD: Twenty patients with a mean age at surgery of 72.6 years, with primary OA of the hip, were investigated preoperatively and at 3, 6, and 12 months postoperatively with the FAS, WOMAC, and SF-36. The responsiveness was calculated as standardized response mean, effect size, and relative efficiency. RESULTS: The pain and function scores of WOMAC and SF-36 showed greater responsiveness than FAS at 3 months. These differences remained at 6 and 12 months postoperatively. The differences between these 3 outcome measures were found to be similar using several methods for calculating responsiveness. CONCLUSION: Self-administered questionnaires like WOMAC and SF-36 are more responsive measures of pain and function than range of motion, performance tests, and observer-administered questions (FAS) following total hip replacement.