The purpose of the study was to determine the prevalence of rotator cuff tears at long-term follow-up after arthroscopic subacromial decompression. Between 1991 and 1994, arthroscopic subacromial decompression was done on 42 shoulders for impingement syndrome. None exhibited signs of a rotator cuff tear. The patients were re-evaluated at a mean postoperative follow-up time of 10 years. At follow-up, the mean age of the patients was 54 years (33 to 69). The evaluation consisted of a clinical examination (including the Constant shoulder score) and an ultrasonographic examination. Only seven patients were found to have developed rotator cuff tears and only one needed a repair procedure. Their mean Constant score was 95. The mean Constant score of 34 patients was 97. One patient refused follow-up owing to a subjective poor result. There were no complications. We conclude that this is an effective intervention for impingement syndrome, protecting the rotator cuff.