The purpose of this study was to investigate the value of ultrasonography in the pre-operative assessment of patients with recurrent post-traumatic, anterior shoulder instability. Forty-four consecutive patients, 44 men and 12 women, with unilateral, post-traumatic, recurrent instability of the shoulder were included in the study. One experienced radiologist examined all patients, using a 5.0 or 7.5 MHz linear-array transducer, with the arm in different positions, one of which was used to provoke apprehension of the shoulder. Special attention was paid to the evaluation of the joint capsule, the anterior labrum, especially in terms of the presence of a Bankart lesion. All patients were subsequently treated surgically. After a diagnostic arthroscopy either an open or arthroscopic stabilisation of the shoulder was performed. Ultrasonography disclosed an unstable anterior labrum (equivalent to a Bankart lesion) in 36 shoulders; the lesion was verified in all 36 shoulders during arthroscopy. In three shoulders, arthroscopy disclosed an injured labrum, which had healed in an anterio-medial position on the scapular neck. In these three shoulders, ultrasonography failed to show any lesion. In five shoulders no Bankart lesion was found at arthroscopy. All these patients had increased shoulder laxity, and ultrasonography did not show any Bankart lesion. Furthermore a judgement of the joint capsule was not possible either. A bony Bankart lesion was found in four shoulders, using both arthroscopy and ultrasonography. The sensitivity of the ultrasonographic evaluation was 92%, and the specificity 100%. The positive predictive value was 100%, and the negative predictive value 63%. Ultrasonography showed a high correlation with the arthroscopic findings, with a high sensitivity and specificity. Therefore, we conclude that US can give important pre-operative information in patients with recurrent, unilateral, post-traumatic, anterior shoulder instability.