A consecutive series of 181 patients with clinical signs of subacromial impingement underwent arthroscopic subacromial decompression (ASD). All patients had the same surgical procedure, and all pathological findings at the arthroscopy were recorded. Ten to 13 years (mean, 11.2) after the procedure, 162 patients (91%) were available for follow-up consisting of clinical examination and the Constant-Murley and DASH scores. The overall mean value of the age correlated Constant score was 77 points. Men had significantly better Constant score than women. The state of the rotator cuff at the index procedure was found to affect the outcome significantly. Patients with isolated full-thickness supraspinatus tears had the best results, followed by those with partial tears, intact cuffs, or large tears involving more than 1 tendon. ASD in the treatment of subacromial impingement yields good long-term results. Small full-thickness supraspinatus tears had the best results, indicating that the ASD might prevent further cuff deterioration and that repair of these lesions may be unnecessary.