Arthroscopic subacromial decompression (ASD) is a method of performing anterior acromioplasty utilizing basic arthroscopic techniques. The procedure is indicated in cases of chronic impingement syndrome that have failed to respond to prolonged conservative management. The purpose of this study is to present an analysis of the 1- to 3-year follow-up results of the initial 50 consecutive cases of ASD that I have performed. Forty (80%) of the cases had advanced stage II impingement without rotator cuff tear. Ten (20%) had full-thickness tears of the rotator cuff. Patients were evaluated pre and postoperatively on the UCLA Shoulder Rating Scale, which includes an assessment of pain, function, range of motion (ROM), strength, and patient satisfaction. Eighty-eight percent of the cases were rated "satisfactory" (excellent or good), and 12% were rated "unsatisfactory" (fair or poor). The procedure is technically demanding, and to achieve a satisfactory result the criteria of open anterior acromioplasty must be met. Arthroscopic subacromial decompression is presented as an alternative to open anterior acromioplasty in advanced stage II and selected cases of stage III impingement syndrome.