In healthy subjects, the shoulder internal rotator muscle strength overrides the external rotators. This has been confirmed in different isokinetic studies showing the ratio of the relative strengths of the internal to external rotators to range from 1.3 to 1.5 points, depending on the study. The authors previously reported a decrease in the relative strength ratio of the internal to external rotators to close to 1 in patients suffering from Neer's impingement syndrome. The aim of the present study was to assess, long after surgery (mean, 44.5 months), the isokinetic strength performance of shoulder rotator muscles in 72 patients who had had operative treatment for chronic subacromial impingement using anterior acromioplasty, sometimes combined with cuff repair surgery. Tests were conducted with a Biodex Multi-Joint System in the plane of the scapula and in 45 degrees abduction at 60 degrees and 180 degrees per second. Peak torque and average power were calculated. The mean ratios of relative strengths of the internal to external rotators ranged from 1.3 to 1.6 points depending on the parameter studied and the test speed. These results indicate that surgery restores normal muscular balance between shoulder rotator muscles affected by the impingement syndrome.