Thirty-seven chronically unstable ankles in thirty-six patients were operated on with use of a Watson-Jones tenodesis. Thirty-four ankles (thirty-three patients) were followed for a mean duration of thirteen years and eight months (range, ten to eighteen years) after the operation. There were nine male and twenty-four female patients. The mean age of the patients was thirty-one years (range, fourteen to fifty-seven years) at the time of the operation and forty-four years (range, twenty-eight to seventy years) at the time of the latest follow-up.At the time of the most recent follow-up evaluation, twenty-seven patients (twenty-eight ankles) were examined directly by one of us and twenty-five patients (twenty-six ankles) also were evaluated radiographically. The other six patients were interviewed, with use of a questionnaire, by telephone. Of the thirty-four ankles, nineteen had an excellent result (grade 1), eleven had a good result (grade 2), three had a fair result (grade 3), and one had a poor result (grade 4) according to the rating system of Good et al. The mean score (and standard deviation) on the ankle-hindfoot scale of the American Orthopaedic Foot and Ankle Society for the twenty-eight ankles that were examined directly by one of us was 90 ± 9.3 points (range, 68 to 100 points). Progression of an exostosis at the edge of the joint was detected in eighteen (69 percent) of the twenty-six ankles that were examined radiographically, but narrowing of the joint space was not seen in any ankle. No relationship was detected between the clinical results and radiographic osteoarthrotic changes or the duration of follow-up. The results did not deteriorate over the long term.