Six hundred one total shoulder arthroplasties and eighty-nine hemiarthroplasties were performed for primary osteoarthritis of the shoulder. Patients were evaluated with a physical examination, Constant score, and radiographic evaluation. The minimum follow-up was 2 years. At follow-up, the Constant score averaged 64 points, the adjusted Constant score averaged 86%, active anterior elevation averaged 130 degrees, and active external rotation averaged 36 degrees for the hemiarthroplasties. The Constant score averaged 70 points, the adjusted Constant score averaged 96%, active anterior elevation averaged 145 degrees, and active external rotation averaged 42 degrees for the total shoulder arthroplasties. Eighty-six percent of hemiarthroplasties and ninety-four percent of total shoulder arthroplasties had good or excellent results. Differences were statistically significant for all parameters. Total shoulder arthroplasty provided better scores for pain, mobility, and activity than hemiarthroplasty. Fifty-six percent of total shoulder arthroplasties had a radiolucent line around the glenoid component. Total shoulder arthroplasty provides results superior to those of hemiarthroplasty in primary osteoarthritis.