We assessed the relative value of lag signs for the evaluation of rotator cuff rupture in a prospective study of 100 consecutive painful shoulders with impingement syndrome, stages 1 to 3. Lag signs were compared with the Jobe and lift-off signs. Three tests were designed to assess the main components of the rotator cuff: the external rotation lag sign (ERLS) for the supraspinatus and the infraspinatus tendons, the drop sign for the infraspinatus, and the internal rotation lag sign (IRLS) for the subscapularis tendon. For assessment of the supraspinatus and infraspinatus the ERLS was less sensitive but more specific than the jobe sign. The drop sign was the least sensitive but was as specific as the ERLS. Partial ruptures of the supraspinatus remained concealed to the ERLS. For assessment of the subscapularis the IRLS was as specific but more sensitive than the lift-off sign. Partial ruptures of the subscapularis tendon could be missed by the lift-off sign but were detected by the IRLS. The magnitude of the lag correlated with the size of the rupture for both the ERLS and the IRLS. Clinical testing for lag signs was efficient, reproducible, and reliable. In patients with little or no restriction of motion it enhanced the accuracy of clinical diagnosis in rotator cuff lesions.