Background: Traumatic anterior shoulder dislocations disrupt the anteroinferior labrum (Bankart lesion), leading to high rates of instability and functional disability, necessitating stabilization. Purpose: To investigate modes and locations of repair failure between simple and horizontal mattress suture configurations after arthroscopic Bankart repair using suture anchors in a cadaveric model. Study Design: Controlled laboratory study. Methods: A total of 48 fresh-frozen human cadaveric shoulders from 48 specimens underwent creation of Bankart lesions from either the 3:00 to 6:00 o’clock position on the right glenoid or the 6:00 to 9:00 o’clock position on the left glenoid. Shoulder laterality between specimens was alternated and randomized to either simple or mattress suture repair configurations. In each shoulder, anchors were placed on the glenoid at the 3:00, 4:30, and 6:00 o’clock positions on the right or 6:00, 7:30, and 9:00 o’clock positions on the left and were secured via standard arthroscopic knot-tying techniques. Specimens were tested in the supine anterior apprehension position using a servohydraulic testing machine that was loaded to failure, simulating a traumatic anterior dislocation. After dislocation, open inspection of specimens was performed, and failure mode and location were documented. Differences in failure mode and location were compared using nominal multivariate generalized estimating equations. Results: Simple suture repairs most frequently failed at the labrum, while mattress suture repair failed at the capsule. Regardless of configuration, repairs failed most commonly at the 3:00 o’clock position on the right shoulder and 9:00 o’clock position on the left shoulder. Compared with mattress suture repairs, simple suture repairs failed at a significantly higher rate at the 6:00 o’clock position. Conclusion: Traumatic anterior shoulder dislocation after arthroscopic Bankart repair in a cadaveric model resulted in simple suture configuration repairs failing most commonly via labral tearing compared with capsular tearing in mattress repairs. Both repair configurations failed predominately at the anterior anchor position, with simple suture repairs failing more commonly at the inferior anchor position. Clinical Relevance: Horizontal mattress suture configurations create a larger area of repair, decreasing the risk of repair failure at the labrum. The extra time required for mattress suture placement at the inferior anchor position is used effectively, resulting in lower biomechanical failure rates.