Reverse total shoulder arthroplasty provides a surgical alternative to standard total shoulder arthroplasty for the treatment of selected complex shoulder problems. The purpose of the present study was to evaluate the effects of etiology on the results of reverse total shoulder arthroplasty.Between May 1995 and June 2003, 240 consecutive reverse total shoulder arthroplasties were performed in 232 patients with an average age of 72.7 years. Patients were grouped according to etiology, and the clinical and radiographic outcomes for each group were measured and compared.One hundred and eighty-six patients with 191 retained reverse total shoulder arthroplasty prostheses were followed for an average of 39.9 months. Overall, the average Constant score improved from 23 points before surgery to 60 points at the time of follow-up and 173 of the 186 patients were satisfied or very satisfied with the result. Although substantial clinical and functional improvement was observed in all etiology groups, patients with primary rotator cuff tear arthropathy, primary osteoarthritis with a rotator cuff tear, and a massive rotator cuff tear had better outcomes, on average, than patients who had posttraumatic arthritis and those managed with revision arthroplasty. Dislocation (fifteen cases) and infection (eight cases) were the most common complications among the 199 shoulders that were followed for two years or were revised prior to the minimum two-year follow-up. Patients who received the reverse prosthesis at the time of a revision arthroplasty had a higher complication rate than did those who received the reverse prosthesis at the time of a primary arthroplasty.The reverse total shoulder arthroplasty prosthesis can produce good results when used for the treatment of a number of other complex shoulder problems in addition to cuff tear arthropathy. Patients with posttraumatic arthritis and those undergoing revision arthroplasty may have less improvement and higher complication rates in comparison with patients with other etiologies. The advanced age of the patients in the present series and the relatively short duration of follow-up suggest that the prosthesis should continue to be used judiciously.