There is no simple method available to identify patients who will develop recurrent instability after an arthroscopic Bankart procedure and who would be better served by an open operation. We carried out a prospective case-control study of 131 consecutive unselected patients with recurrent anterior shoulder instability who underwent this procedure using suture anchors. At follow-up after a mean of 31.2 months (24 to 52) 19 (14.5%) had recurrent instability. The following risk factors were identified: patient age under 20 years at the time of surgery; involvement in competitive or contact sports or those involving forced overhead activity; shoulder hyperlaxity; a Hill-Sachs lesion present on an anteroposterior radiograph of the shoulder in external rotation and/or loss of the sclerotic inferior glenoid contour. These factors were integrated in a 10-point pre-operative instability severity index score and tested retrospectively on the same population. Patients with a score over 6 points had an unacceptable recurrence risk of 70% (p < 0.001). On this basis we believe that an arthroscopic Bankart repair is contraindicated in these patients, to whom we now suggest a Bristow-Latarjet procedure instead.