Since the mid 1980s, sonography has been used to evaluate the rotator cuff. It is inexpensive, well tolerated, rapidly performed, and accurate. With the recent improvements in imaging equipment and refinements in scanning technique, an increasing number of radiologists are performing shoulder sonography. This article emphasizes the pertinent musculoskeletal anatomy, sonographic technique, normal sonographic anatomy, pathophysiology of rotator cuff and biceps tendon disease, sonographic findings of rotator cuff tears, and biceps tendon pathology. The accuracy of ultrasound in diagnosing rotator cuff tears and miscellaneous abnormalities that can be detected with ultrasound also are discussed.