140 patients with shoulder impingement syndrome were randomized to undergo arthroscopic acromioplasty with exercise rehabilitation, or to participate in a supervised exercise program alone. The purpose of this study was to determine whether arthroscopic acromioplasty is superior to common nonsurgical treatment in terms of long-term pain relief, and to determine whether the treatments were less effective among certain subgroups. Results indicated that both treatments led to significant improvements in pain relief, and that there was no significant difference in improvement between groups at any time. Results also suggested that symptom duration, marital status, lengthy sick leaves, impingement of the radiological acromioclavicular joint, and lack of professional education affected the efficacy of the included treatments with respect to pain relief.