Background: Little information is available on the American Orthopaedic Foot and Ankle Society (AOFAS) outcome tool and its capacity to show changes and improvement in function of patients without a floor or ceiling effect. The purpose of the study was to compare results from the Musculoskeletal Functional Assessment (MFA) and AOFAS outcome tools in a population undergoing a total ankle replacement. Methods: Prospective data was collected on 154 patients preoperatively and at 6, 12, and 24 months after surgery. An analysis was performed between both and within each tool across the time of followup. Results: No ceiling or floor effect was noticed on the AOFAS outcome tool. Its capacity for discrimination and to observe changes in pain and function are acceptable. No correlation between the AOFAS categories of pain and function and the MFA domain of well being could be found. Both outcome tools presented similar responses. Conclusions: Though the AOFAS outcome tool seems to have enough sensitivity to analyze pain and function during a postoperative period, the authors strongly recommend the use of an alternative outcome tool to better understand and delineate the patient's level of function and effect of treatment on their quality of life. Clinical Relevance: These data improve the understanding of and indications for the AOFAS outcome tool. They confirm the AOFAS questionnaire as a tool with enough discriminatory capacity to assess patient improvement and also point out the weaknesses of the questionnaire and the importance of collecting parallel data with other available outcome tools to better understand patient function and quality of life.