It is difficult to determine the size and localization of rotator cuff tears preoperatively. But with the special arthrographic technique, a diagnosis with about 80% accuracy was possible in 65 surgically confirmed rotator cuff tears. With this technique, 22 massive cuff tears were found in conservatively treated patients. In these patients, the plain roentgenograms obtained at the initial examination were also analyzed. The roentgenographic findings included narrowing of the acromiohumeral interval and degenerative changes of the humeral head, the tuberosities, the acromion, the acromioclavicular joint, and the glenohumeral joint. Based on these data, five roentgenographic grades of massive cuff tears were identified. Of seven patients with massive tears, which had been treated conservatively and followed for more than eight years, the roentgenographic grades advanced in five. One shoulder progressed to cuff-tear arthropathy. Based on these observations, it is proposed that the following pathogenetic mechanisms are responsible for the progressive roentgenographic changes: (1) arm elevation in activities of daily living, (2) rupture of the long head of biceps tendon, (3) the abnormal fulcrum of the humeral head against the acromion and the coracoacromial ligament, and (4) the weakness of external rotation. A massive cuff tear will progress to cuff-tear arthropathy, with each step of progression accompanied by characteristic roentgenographic changes.