A detailed computer-assisted evaluation of eighty-nine patients whose shoulders were surgically treated for anterior instability was done. Three types of anterior instability of the shoulder were identified: Type I, subluxation without prior dislocation; Type II, recurrent dislocation with interval subluxation; and Type III, recurrent dislocation without interval subluxation. This series included fifty patients with Type-I, twenty-nine with Type-II, and ten patients with Type-III instability. Selected variables from the computer analysis of forty-five preoperative and post-operative parameters were related to the type of instability diagnosed preoperatively. The surgical procedure used in all shoulders was a modification of the Bankart procedure. Chronic glenohumeral instability is a disabling entity which can be controlled by surgical stabilization of the anterior capsule to the glenoid rim.