OBJECTIVE: To analyze the dimensionality of 2 self-report outcome measures (Foot/Ankle Disability Index [FADI] and Short-Form [SF]-36), 3 biomechanical measures (stance and step symmetry measures, gait speed, and step width), 2 physical-performance measures (timed get-up and go [TUG] and 4-square step test [4SST]), and 1 clinician-report outcome measure (American Orthopaedic Foot and Ankle Society [AOFAS] Hindfoot Scale) in a patient population with unilateral ankle arthritis. These measures captured the following functions: mobility and speed, pain and its relationship to function, social integration, and symmetry and efficiency of gait. DESIGN: Case series design. SETTING: Biomechanical research laboratory adjacent to a busy orthopedic clinical practice. PATIENTS: Seventy-nine consecutive patients with unilateral traumatic arthritis who were candidates for a total ankle replacement. METHODS: An exploratory factor analysis with oblimin rotation was performed to determine the dimensions of the physical performance, biomechanical, self-report, and clinician-report measures. MAIN OUTCOME MEASUREMENTS: Outcomes measures included the SF-36 and pertinent subscales, gait speed, the 4SST, the TUG, the FADI, the AOFAS Hindfoot Scale, and biomechanical measures of step width, step symmetry, and stance symmetry. RESULTS: Four distinct dimensions were captured during factor analysis. Factor 1 included the TUG, gait speed, the 4SST, and step width; factor 2 included the FADI, the SF-36 bodily pain score, and the SF-36 physical function score; factor 3 included the biomechanical scores of stance symmetry ratio and the step symmetry ratio; and factor 4 included SF-36 social functioning and the AOFAS Hindfoot Scale. CONCLUSIONS: Findings suggest that various outcome measures for the ankle capture different dimensions and should be considered when evaluating the presence of disability or long-term change in outcome.