Occult shoulder instability is recognized as a significant contributor to shoulder dysfunction in throwing athletes. Diagnosis of occult instability by physical examination remains challenging. The anterior release test is a test for physical examination of the shoulder. It was developed to facilitate detection of occult anterior instability. One hundred shoulders were examined preoperatively by the same examiner. Based on surgical findings, the shoulders were classified as anterior instability or other. The results of examination were compared with the operative findings. Sensitivity was calculated as 91.9%, specificity 88.9%, positive predictive value 87.1%, negative predictive value 93.0%, and accuracy 90.2%. The anterior release test is a reliable and reproducible test for the detection of the unstable shoulder.