Twenty-four thumbs of twenty-two patients were evaluated at an average of nine years (range, eight to eleven years) after a ligament reconstruction-tendon interposition arthroplasty for osteoarthrosis at the base of the thumb. The same group had also been examined two and six years postoperatively. The procedure had been performed as a primary operation in twenty-one thumbs and as a revision of a failed implant arthroplasty in three. Twenty-one (95 per cent) of the twenty-two patients had excellent relief of pain and were satisfied with the outcome. The average grip strength increased ten kilograms (p < 0.005), reflecting a 93 per cent improvement compared with the preoperative values. Similarly, the average tip pinch strength steadily improved, with an increase at the most recent examination of nearly one kilogram (p < 0.005) (65 per cent improvement). Improvements in the average key pinch strength, however, were first noted at the six-year follow-up examination and then tapered slightly; the most recent values reflected an average gain of 34 per cent but were not significantly different from the preoperative values. The tip of twenty-two (92 per cent) of the twenty-four thumbs was able to touch the base of the little finger, and the most recent average web angle (40 degrees) was unchanged from the value at the two-year follow-up examination. Stress radiographs showed an average subluxation of the metacarpal base of 11 per cent at nine years compared with 7 and 8 per cent at two and six years, respectively. Similarly, these radiographs demonstrated an average loss of height of the arthroplasty space of 13 per cent at nine years compared with 11 per cent at both of the earlier follow-up examinations. This modest deterioration of radiographic parameters was not predictive of an unsatisfactory outcome. The ligament reconstruction-tendon interposition arthroplasty provided a stable and functional reconstruction of the thumb, resulting in excellent relief of pain and a significant increase in strength for as long as eleven years after the procedure.