In a controlled clinical prospective study, 43 consecutive patients (43 shoulders) with subacromial impingement resistant to conservative therapy and without full-thickness rotator cuff tears underwent arthroscopic subacromial decompression. The patients were randomized to either self-training or physiotherapist-guided rehabilitation for immediate postoperative rehabilitation. Postoperative follow-up was performed by an independent observer after 3, 6, and 12 months. With the use of the Constant score for evaluation of functional outcome, patients training themselves improved from a mean 53 points (range 26 to 81 points) to a mean 79 points (range 45 to 100) points after 12 months. Physiotherapist-supervised patients improved from a mean 54 points (range 20 to 90 points) to a mean 80 points (range 40 to 100 points). The self-training patients returned to work after a mean 8.5 weeks (range 1 to 14 weeks), whereas the physiotherapist-supervised patients returned to work after a mean 8 weeks (range 3 to 13 weeks). No statistical difference was found between the 2 rehabilitation methods. This study was unable to show any beneficial effect of physiotherapist-supervised rehabilitation after arthroscopic subacromial decompression of the shoulder.