In 200 shoulders from cadavera, we studied the pathological changes on the undersurface of the acromion as associated with tears of the rotator cuff. After radiographic and histological analysis, we found that in the specimens that had a partial tear of the cuff the undersurface of the acromion was almost intact. Although a lesion in the anterior one-third of the undersurface of the acromion was always associated with a tear of the cuff, the reverse was not true. We concluded that the pathogenesis of most of the tears probably is a degenerative process.