68 patients underwent arthroscopic subacromial decompression for shoulder impingement syndrome. Patients were evaluated preoperatively, at 3 weeks and 3 months post operatively using the Constant score. Mean preoperative Constant score was 46. 5 (34–67), at 3 weeks 65. 8 (40–86), and at 3 months 82. 4 (50–99). There was no correlation between the impingement grade, presence of a cuff tear or acromioclavicular joint involvement, and a significant poorer outcome. Arthroscopic subacromial decompression is a reliable method of improving the functional ability of patients with subacromial impingement syndrome, with a 20 point increase in the Constant score at 3 weeks post surgery, rising to a 40 point increase at 3 months. Patients can therefore be counselled that they will make a significant functional improvement in a short time after surgery.