100 thumbs with primary osteoarthrosis of the joints of the trapezium were treated by trapeziectomy and a FCR sling arthroplasty to reconstruct a first intermetacarpal ligament by the method described by Burton and Pellegrini (1986). Pain at rest remained in five. Some pain at or after exertion persisted in 46, and 49 became completely pain-free. 88 were satisfied with the procedure and there was a significant increase in pinch strength and in the ability to perform activities of daily life. It has become our preferred procedure for treating osteoarthrosis of the basal joint of the thumb.