The outcome of 80 glenohumeral arthroplasties with the Neer prosthesis in 77 patients with degenerative or inflammatory shoulder disease was evaluated after a mean follow-up of three years five months. The arthroplasties were performed because of intractable pain and functional disability due to destruction of the glenohumeral joint. The postoperative rehabilitation program focused on full recovery of joint motion and function in 65 cases and on joint stability with partial recovery of joint motion and function in 15 cases. According to the criteria developed by Neer, the outcome was excellent or satisfactory in 75% of cases and unsatisfactory in 25%. Constant's scores adjusted for age and gender varied widely across diagnostic categories, from a high of 76% in centered glenohumeral osteoarthritis (n = 40) to lows of 59% in rheumatoid arthritis (n = 21) and 45% in posttraumatic osteoarthritis (n = 10) or eccentric osteoarthritis due to cuff disruption (n = 9). At reevaluation, 70% of patients had little or no pain and 90% were satisfied with the outcome. The mean increase in flexion of the arm (39 degrees) was markedly influenced by the diagnosis. The increases in lateral rotation (mean 35 degrees) and medial rotation (four vertebral levels) of the arm were especially appreciated by the patients as having a very beneficial effect on the ability to perform everyday tasks. Complications included instability in three cases (two anterior dislocations and one posterior dislocation), glenoid component loosening in 11 cases (of which only four required reoperation) and rotator cuff tear in eight cases. Our results add to the existing evidence that nonconstrained shoulder implants, such as the Neer prosthesis, are both safe and effective in alleviating pain and improving joint function. They should be used in patients with refractory pain, disability due to restrictions in external and medial rotation of the arm and roentgenographic evidence of glenohumeral joint space loss.