OBJECTIVES: The goal of this study was to evaluate the relationship amongst patient expectations and outcomes measured by health related quality of life (HRQOL) questionnaires at 12 months after surgery in patient undergoing total joint replacement. METHODS: In this prospective study took part 15 hospitals. The questionnaire was sent to the patients while waiting for total hip (THR) or knee replacement (TKR) and 12 months post-surgery. In this questionnaire were included specific HRQOL instrument WOMAC, two generic instruments SF-12 and EQ-5D and eight questions about patient’s expectations which were grouped into physic-functional (5), emotional (2) and psychological expectations (1).The responses of the expectation questions were graded on a 5 point Likert scale ranging from “no expectations” to “a lot of expectations”. Given the skewed distribution of the response patterns these were categorized from 1 to 3 in “no”, “quite” and “a lot of expectations”. The ANOVA test was used to evaluate the impact of the expectations on the measured outcomes. RESULTS: There were 884 patients (360 hips and 524 knees) who replied the two times. In all the physic-functional expectations items patients showed statistically significant improvements  in all HRQOL dimensions except in the Mental Component Summary (MCS) of the SF-12, observing an ascending gradient, so the higher the prior-surgery expectations are, the greater the improvement is, at 12 months post-surgery. Regarding the two questions about social expectations, in both of them the results were equal to the physic-functional expectations in all dimensions. The question about psychological expectations keeps on showing this significant improvement in all the dimensions with the same ascending gradient CONCLUSIONS: Patient expectations prior-surgery were important predictors of improvement outcomes in health related quality of life at 12 months after THR and TKR.