BACKGROUND: Adjustment of patient satisfaction scores for case-mix variables such as age and sex may lead to overadjustment. The patient's tendency to rate healthcare positively or negatively may be the only variable that should be adjusted to improve the comparability of satisfaction scores between healthcare providers. OBJECTIVE: To develop a measure of "rating tendency", assess its stability over time, explore its distribution across subgroups of patients and its association with patient opinion scores. Design and SUBJECTS: A scale based on 10 hypothetical scenarios describing hospital care episodes was developed. It was administered both before and after hospitalisation to 203 patients programmed for elective orthopaedic surgery in a Swiss teaching hospital. A problem score regarding the actual hospitalisation was obtained at follow-up. RESULTS: The rating tendency scale had good internal consistency (Cronbach alpha 0.85), and factor analysis confirmed that it measured a single underlying concept. However, the correlation between prehospitalisation and posthospitalisation measures was moderate (intraclass correlation coefficient 0.55, p<0.001), as was the correlation with the hospitalisation problem score (Spearman r = -0.22, p = 0.002). The pattern of rating tendency across subgroups of respondents mirrored the pattern of problem scores. Adjusting for the rating tendency had little effect on comparisons of problem scores between subgroups of patients, all of whom were treated at the same hospital. CONCLUSIONS: A patient's "rating tendency" can be measured using a reliable 10-item scale. The utility of adjusting satisfaction scores for rating tendency when comparing hospitals remains to be tested.