The aim of this investigation was to evaluate the long-term outcome of arthroscopic subacromial decompression (ASD) in patients with primary impingement syndrome stage II and early stage III. Ninety-five patients (105 shoulders, 48 female), mean age 54 years (range 26-69), who had undergone surgery between 1996 and 1999, were included. Pain intensity during activity and at rest, patient satisfaction, active range of motion (ROM), muscular strength and shoulder function using the Constant score were evaluated. Fifty-three (50%) shoulders were pain-free (Visual Analogue Scale < or = 10 mm) during activity and 72 (68%) shoulders were pain-free at rest. Sixty-one (58%) patients stated that they were very satisfied and 27 (25%) were quite satisfied with regard to their current shoulder function. Shoulders were divided into Group 1: Pain-free patients (n = 53), Group 2: Patients with shoulder pain and no arthropathy (n = 41) and Group 3: Patients with shoulder pain and arthropathy (n = 11). The groups had average active ROM of 157 degrees, 135 degrees and 117 degrees, respectively, in abduction and 97 degrees, 79 degrees, and 68 degrees in external rotation. The average strength in elevation in the scapular plane was 7.4, 5.8 and 3.9 kg, respectively, whereas the mean value in external rotation was 8.4, 7.9 and 5.3 kg, respectively. The Constant score had a mean value of 87, 69 and 59 points in the three groups, respectively. Eleven shoulders have undergone re-operation, one after a new trauma. We conclude that ASD is a valuable procedure. Patients expressed a high degree of satisfaction with shoulder function 8-11 years after ASD.