Forty-five flexor carpi radialis (FCR) tendon interposition arthroplasties of the trapezium for the treatment of carpometacarpal osteoarthritis were reviewed. The average follow-up period was 103 months (range, 22-213 months). Pain was reduced in 42 (93%) of the cases, Mobility was equal to that of the unoperated side. Key pinch and grip strengths compared to the unoperated thumb measured 86% and 90%, respectively. The mean distance between the scaphoid and the base of the first metacarpal bone was 7 mm (range, 2-12 mm). Function was improved in 39 (87%) of the cases, and in 42 (93%) of the cases the overall results were satisfactory. The results of this study show that FCR tendon interposition arthroplasty gives satisfactory long-term results.