We studied seven patients who had isolated loss of the proximal attachment of the tendon of the long head of the biceps brachii, documented operatively or with magnetic resonance imaging, in order to identify and measure superior translation of the humeral head on the glenoid. Four true anteroposterior radiographs were made of both shoulders, before and after the operation, with 0, 45, 90, and 120 degrees of humeral abduction in the scapular plane. Four patients were managed with arthroscopic acromioplasty with an open biceps tenodesis; one, with open biceps tenodesis alone; and one, with debridement of a ruptured biceps stump; the remaining patient was managed non-operatively. Two to six millimeters of superior translation of the humeral head was noted in each patient in all positions of humeral abduction except 0 degrees. This translation was significant compared with the contralateral (control) shoulder. Kappa statistical analysis showed excellent reproducibility and interobserver reliability of the technique of radiographic measurement. The results of this study support the role of the tendon of the long head of the biceps brachii as a stabilizer of the humeral head in the glenoid during abduction of the shoulder in the scapular plane.