One hundred consecutive patients with symptoms of chronic subacromial impingement syndrome were evaluated by both arthrography and magnetic resonance imaging (MRI) techniques. By comparing intermediate and T2 weighted images, the ability to identify the normal and abnormal anatomy of the rotator cuff with the MRI was excellent. All 51 patients with arthrogram-proven rotator cuff tears had abnormal MRI scans (100% sensitivity). However, six of the 49 patients with normal arthrograms had abnormal MRI scans (88% specificity). At arthroscopy, four of these patients were found to have moderate to severe partial thickness rotator cuff tears. These findings indicate that in patients with longstanding subacromial impingement syndrome the MRI has an exceptionally high sensitivity for damage to the rotator cuff.