The use of shoulder ultrasound as an imaging modality has recently gained widespread attention; however, the ability of ultrasound to diagnose long head of the biceps tendon pathology accurately still remains unclear. The biceps tendons in 71 patients were prospectively evaluated by comparison of standard ultrasonographic and arthroscopic examinations. Arthroscopic examination was used as the gold standard comparison. Ultrasound showed a 100% specificity and 96% sensitivity for subluxation or dislocation. Ultrasound detected all complete ruptures of the biceps tendon but detected none of the 23 partial-thickness tears. Overall, ultrasound diagnosed 35 of 36 normal biceps tendons (specificity, 97%) and 17 of 35 abnormal biceps tendons (sensitivity, 49%). Ultrasound can reliably diagnose complete rupture, subluxation, or dislocation of the biceps tendon. It is not reliable for detecting intraarticular partial-thickness tears.