140 patients with shoulder impingement syndrome were randomized to either a supervised exercise program alone or to arthroscopic acromioplasty followed with a similar exercise program. The purpose of this subgroup analysis study was to determine which patients (from either the arthroscopic acromioplasty and exercise therapy group, or the group treated solely with exercise therapy) are effectively treated for shoulder impingement syndrome when followed up at 2 and 5 years. Findings showed similar results between the patients who underwent operative treatment and the group that underwent conservative treatment. Furthermore, arthroscopic acromioplasty did not appear to improve results in patients who were originally allocated to exercise therapy alone and were unsatisfied with outcome following conservative management.