Seventeen patients who had osteoarthritis of the glenohumeral joint after surgery for glenohumeral instability underwent prosthetic replacement. Thirteen men and four women with an average age of 43 years were studied. The interval from the initial instability repair to prosthetic replacement averaged 16 years. Before the operation all patients had severe functional disability caused by pain and limited range of motion, especially external rotation. Twelve patients underwent total shoulder replacement, and five patients underwent humeral head replacement. At an average follow-up period of 3 years, 13 (77%) satisfactory results and four (23%) unsatisfactory results were obtained. Pain was relieved in 16 (94%) of the 17 patients. Range of motion improved by an average of 37 degrees of elevation and 53 degrees of external rotation. Previous surgery had distorted the anatomy, and special techniques were required to correct anterior soft-tissue contracture and to compensate for posterior glenoid bone loss.