Four hundred twenty humeri were measured to determine humeral head retroversion and its relation to the location of the bicipital groove. Average head retroversion was found to be 28.3 degrees (+/- 13.2 degrees), and the angular orientation of the bicipital groove referenced to the transepicondylar axis was 55.5 degrees (+/- 13.8 degrees). The average difference between these angular orientations was 27.3 degrees (+/- 14.2 degrees). This result implies that the bicipital groove can be used as a landmark for prosthetic stem positioning in shoulder arthroplasty if the center of the lateral aspect of the stem is posteriorly offset approximately 30 degrees from the center of the groove. However, because of the appreciable variation in these averages, the use of the bicipital groove as a reference can result in a significant error of humeral stem alignment, which should be considered when determining the retroversion for a particular patient.