Background. The Musculoskeletal Tumor Society (MSTS) scoring system measures function and is commonly used but criticized because it was developed to be completed by the clinician and not by the patient. We therefore evaluated if there is a difference between patient and clinician reported function using the MSTS score. Methods. 128 patients with bone metastasis of the lower (n = 100) and upper (n = 28) extremity completed the MSTS score. The MSTS score consists of six domains, scored on a 0 to 5 scale and transformed into an overall score ranging from 0 to 100% with a higher score indicating better function. The MSTS score was also derived from clinicians' reports in the medical record. Results. The median age was 63 years (interquartile range [IQR]: 55-71) and the study included 74 (58%) women. We found that the clinicians' MSTS score (median: 65, IQR: 49-83) overestimated the function as compared to the patient perceived score (median: 57, IQR: 40-70) by 8 points (p < 0.001). Conclusion. Clinician reports overestimate function as compared to the patient perceived score. This is important for acknowledging when informing patients about the expected outcome of treatment and for understanding patients' perceptions.