INTRODUCTION: In November 2011, the Knee Society published its new KSS score to evaluate objective clinical data and also patient expectations, satisfaction and knee function during various physical activities before and after total knee arthroplasty (TKA). We undertook the French cross-cultural adaptation of this scoring system according to current recommendations. HYPOTHESIS: The French version of the new KSS score is a consistent, feasible, reliable and discriminating score. PATIENTS AND METHODS: Eighty patients with knee osteoarthritis were recruited from two centers: one group of 40 patients had a TKA indication, while the other group of 40 patients had an indication for conservative treatment. After the new KSS score was translated and back-translated, it was compared to three other validated instruments (KOOS, AMIQUAL and SF-12) to determine construct validity, discriminating power, feasibility in terms of response rate and existence of floor or ceiling effect, internal consistency with Chronbach's alpha and reliability based on reproducibility and sensitivity to change (responsiveness). RESULTS: Due to missing data, two cases were eliminated. We found that the score could discriminate between groups; it had a nearly 100% response rate, a ceiling effect in the "expectations" domain, satisfactory Chronbach's alpha, excellent reproducibility and good responsiveness. DISCUSSION: These results confirm that the French version of the new KSS score is reliable, feasible, discriminating, consistent and responsive. The novelty of this scoring system resides in the "expectations" and "satisfaction" domains, its availability as a self-assessment questionnaire and the evaluation of function during various activities. LEVEL OF PROOF, TYPE OF STUDY: Level III.