The hip-rating questionnaire was developed for the assessment of the outcome of total hip replacement. The purpose of this study was to evaluate its reproducibility, validity, and responsiveness. The questionnaire uses a 100-point scale in which equal weight is given to the domains of global or over-all impact of arthritis, pain, walking, and function. Ninety-eight patients were enrolled in the prospective study and have been followed for at least three months; sixty-two patients have been followed for six months; and forty-two patients have been followed for one year. Reproducibility was tested with the use of the kappa statistic in fifty patients whose condition was stable clinically, and it was found to be good or excellent both for individual questions and for the total score. The validity of the questionnaire was assessed by comparison with the scores from a six-minute walking-distance test and arthritis impact-measurement scales. The result of the six-minute walking-distance test correlated with the patient's response concerning walking distance on the hip-rating questionnaire. The score for pain from the hip-rating questionnaire correlated well with the score for pain from the arthritis impact-measurement scales, and the total score from the hip-rating questionnaire correlated well with the total score from the arthritis impact-measurement scales. The score on the hip-rating questionnaire was responsive to the change in the clinical condition of the patient, as indicated by a favorable index of responsiveness. The results of the questionnaire were sensitive enough to demonstrate differences among treatment groups with relatively small sample sizes. This questionnaire has the characteristics of a useful instrument for assessment of outcomes, such as that after an operation.