Compression studies were conducted on the ligamentous thoracolumbar spines of fresh human male cadavers. For comparison, forces were applied to the posterior upper thoracic region of intact seated cadavers. Since thoracolumbar flexion injury routinely involves ligament failure and vertebral body wedge compression fractures, studies were conducted on single vertebral bodies and isolated ligaments. Similar studies were conducted in isolated monkey ligaments. The intact and ligamentous thoracolumbar spines failed predominantly in the region of the thoracolumbar junction at forces from 1113-5110 N. For both the human and monkey cadavers, the anterior longitudinal ligament was the strongest. The human ligaments were 2-5 times stronger than those of the monkey.