We examined the early results of using an open bone block technique to stabilize the glenohumeral joint with chronic instability related to bony deficiency of the glenoid. Fifteen patients with anteroinferior glenoid bone loss on preoperative computed tomography underwent diagnostic shoulder arthroscopy (for evaluation of glenoid bony deficiency) and then open bone block augmentation of the anteroinferior glenoid rim. Clinical follow-up of 10 patients at a mean of 25 months showed a mean postoperative Constant score of 94 (range, 32-100), a mean University of California Los Angeles score of 32 (range, 9-35), and a mean American Shoulder and Elbow Surgeons score of 83 (range, 47-100). Mean postoperative forward flexion was 172 degrees, mean postoperative external rotation with the arm at the side was 60 degrees , mean postoperative external rotation with the arm abducted 90 degrees was 91 degrees, and postoperative internal rotation ranged from the level of the anterosuperior iliac spine (minimal external rotation) to the T6 spinal level. Bone block stabilization is an effective treatment in patients with chronic shoulder instability--a difficult population.