Thirty-eight thumbs in 35 patients with painful osteoarthritis of the thumb basal joint were treated by trapezium excision and abductor pollicis longus tendon interposition arthroplasty. Long-term results were obtained from all patients by subjective evaluation and 29 patients were re-examined 1 to 11 years after surgery (mean, 6 years). The overall result was excellent or good in 79% of the cases and 76% of the patients reported good or excellent pain relief. In 6 cases (16%) surgery provided no improvement. The range of shortening of the first ray was from 2 to 10 mm (mean, 7 mm). Grip and pinch strengths were measured, but the results were variable and consequently not informative. On the basis of our results we recommend abductor pollicis longus tendon interposition arthroplasty for the treatment of osteoarthritis of the thumb basal joint.