Total joint replacements are some of the most successful medical devices developed over the last fifty years. They enable millions of people to remain ambulatory and pain free, with minimal risk. In 2002, over 200,000 total hip replacements, 350,000 total knee replacements, and 25,000 total or partial shoulder replacements were performed in the United States (HCUP data). Future use will likely be even higher: it is estimated that by the year 2020, the population 65 and over in developed countries will increase by 71%. Existing studies do not provide adequate prospective data to evaluate long-term outcomes. HSS is a world leader in total joint replacement including total shoulder arthroplasty. However, there is no systematic follow-up or evaluation of patients who have their shoulders replaced here. The purpose of this study is to establish a prospective cohort of HSS total shoulder arthroplasty to evaluate predictors of outcome, causes of failure and to allow ongoing evaluation of the results of our patients over time.