This study's objective is to elucidate the relationship between acromial spur formation and rotator cuff pathology or aging. The subjects comprised 1029 shoulders in control, cadaveric, and operative groups. A radiograph in the supraspinatus outlet view was taken in all subjects. The lengths of the incident spurs were measured and classified into 3 sizes (small, <5 mm; medium, <10 mm; and large, > or =10 mm). The rotator cuff was macroscopically classified as normal or as having bursal-side fraying, joint-side tear, intratendinous tear, bursal-side tear, complete tear limited to the supraspinatus tendon, or massive tear. In the control group, the overall incidence of spurs and spur size increased with advancing age (P < .001), but the majority of spurs were small (<5 mm). In the cadaveric group, the overall incidence did not correlate with advancing age (P > .05). However, spur size increased with age in subjects aged 50 years or older (P < .001). The incidence of spurs in rotator cuffs with bursal-side tears was highest and was significantly higher than that in normal cuffs and cuffs with bursal-side fraying and intratendinous tears. We observed 40% of medium spurs and 69% of large spurs in cases with bursal-side tears, complete tears limited to the supraspinatus tendon, and massive tears. In the operative group, the overall incidence correlated to advancing age (P < .001), reaching 80% or more in subjects aged 30 years or older. In addition, the size of spurs was larger than that in the other 2 groups in all age groups with few exceptions (P < .05). Small spurs were associated with advancing age. Morphologic change to the bursal side of the rotator cuff may enhance spur growth. The presence of a small spur has no diagnostic value for rotator cuff tears. Spurs measuring 5 mm or more, however, are of diagnostic value because of their high rate of association with bursal-side tear, complete tears limited to the supraspinatus tendon, or massive tears.