INTRODUCTION: Malignant tumors of the extremities are uncommon. Their surgical treatment, whether conservative or not, may cause sequelae. Functional assessment of patients is essential for research purposes, but also follow-ups and adaptation of treatments. The Musculoskeletal Tumor Society Rating Scale (MSTS) is a disease-specific functional scoring system often used in English literature. Currently, no studies have been published on a valid French translation of the MSTS, whether for the lower or upper extremities. We, therefore, conducted a prospective study to answer the following questions: (1) Are the proposed adapted French versions of the MSTS valid? (2) Do the psychometric properties of the two versions obtained make their use relevant? MATERIALS AND METHODS: The translation and cross-cultural adaptation were carried out following the recommendations of Beaton and Guillemin to obtain two versions: one for patients who had undergone upper extremity surgery (MSTS-UE) and one for those who had undergone lower extremity surgery (MSTS-LE). A prospective multicenter cohort study was then carried out to analyze the psychometric properties of these two versions. RESULTS: A total of 250 patients from 3 referral centers were enrolled in this study. A confirmatory factor analysis (CFA) demonstrated that the two French versions of the MSTS (MSTS-LE and MSTS-UE) were a good fit with a root mean square error of approximation (RMSEA)<0.08 and a comparative fit index (CFI)>0.90. The psychometric properties of the two versions were validated with internal consistency (Cronbach alpha>0.7), convergent validity of each item with its score (> 0.4), and sufficient criterion validity (Pearson correlation coefficient>0.4). The discriminant validity analysis showed that there was a significant correlation between each version and the performance status (PS) (p<0.05). CONCLUSION: This study produced a French version of the MSTS scoring system and validated the psychometric properties of the two versions obtained (MSTS-UE and MSTS-LE). Therefore, the French MSTS scoring system is a valid measurement that can be used in international studies. LEVEL OF EVIDENCE: I.