Tendon interposition resection arthroplasty of the trapezium is a valuable tool in treating osteoarthrosis of the first carpometacarpal joint. A previously unreported modification of such an operation is described in which a part of the abductor pollicis longus tendon is used as an interposition material. This technique was employed in a series of thirty-nine thumbs. After a minimal follow-up period of 2 years, the results of the operation are graded excellent in 48% of the patients, good in 35%, and average in the rest. Grip strength, as well as pinch strength, is about three quarters of the normal average. No patient needed a further operation.