The goal of this study was to document whether an association exists between shoulder dislocation and the development of arthosis and to quantify this association, if present. Patients with osteoarthrosis who had undergone hemi-shoulder or total shoulder arthroplasty (TSA) were studied. Patients who had undergone total knee arhroplasty for arhrosis and who had no history of shoulder symptoms served as control subjects. All patients were asked if they had ever sustained a shoulder dislocation. Ninety-one TSA patients and 282 control subjects responded. The odds ratio for developing arthrosis after a shoulder dislocation was 19.3 (P = .000006). With 5 patients who had shoulder surgery prior to TSA excluded, the odds ratio was 10.5 (P = .003). The risk of developing severe arthrosis of the shoulder is between 10 and 20 times greater for individuals who have had a dislocation of the shoulder.