We sought to determine the accuracy of ultrasound for the preoperative evaluation of shoulder impingement syndrome, rotator cuff tear, and abnormalities of the long head of the biceps tendon. The findings in 42 consecutive surgical cases were compared with the preoperative sonographic readings. Ultrasound detected all of the 10 full-thickness cuff tears identified at surgery (sensitivity 1.0, specificity 0.97) but detected only 6 of 13 partial-thickness cuff tears (sensitivity 0.46, specificity 0.97). A full-thickness tear was falsely diagnosed in one case of severe cuff abrasion. Dynamic scan criteria correctly diagnosed impingement in 27 of 34 cases (sensitivity 0.79, positive predictive value 0.96). Abnormalities of the long head of the biceps were accurately diagnosed with the exception of low-grade tendinitis and the superior labral tear, anterior to posterior, lesion. We concluded that ultrasound is a sensitive and accurate method of identifying patients with full-thickness tears of the rotator cuff, extracapsular biceps tendon pathology, or both. Dynamic ultrasound can help confirm, but not exclude, a clinical diagnosis of impingement.