We studied the validity and reliability of the Foot and Ankle Outcome Score (FAOS) when used to evaluate the outcome of 213 patients (mean age 40 years, 85 females) who underwent anatomical reconstruction of the lateral ankle ligaments with an average postoperative follow-up of 12 years (range, three to 24 years). The FAOS is a 42-item questionnaire assessing patient-relevant outcomes in five separate subscales (Pain, Other Symptoms, Activities of Daily Living, Sport and Recreation Function, Foot- and Ankle-Related Quality of Life). The FAOS met set criteria of validity and reliability. The FAOS appears to be useful for the evaluation of patient-relevant outcomes related to ankle reconstruction.