Several reports on burst fractures of the thoracolumbar spine have noted that the neural canal encroachment caused by bone in the canal did not correlate with the neurologic status of the patient. But in the thoracolumbar spine the average percent compromise was significantly higher in those patients with complete and incomplete lesions, compared with those patients with no neural deficits. In this study, we evaluated 38 patients with unstable thoracolumbar fractures, operated from March 1989 to February 1993 to know the amount of neural canal compromise, demonstrated on computed tomography scans with neurologic status, level of injury and type of fractures. Among them 22 patients had neurologic deficit and 16 did not neurologic deficit. The results were as follows; 1. 19(76%) of 22 patients with disruption of the posterior spinal elements had neurologic defictis. 2. In the group with neurologic deficits, the stenotic ratio was 44% at the epiconus level, 55% at the conus medullaris, level and 63% at the cauda equna level. 3. The average A-P diameter of the bony fragments retropulsed into the spinal canal was 4.5mm at the epiconus level, 5.2mm at the conus medullaris level and 6.0mm at the cauda equina level. 4. Unstable bursting fracture and fracture dislocation showed higher incidence of neurologic injury and percentage of spinal stenotic ratio than those of flexion distraction and wedge compression fracture. In conclusion, the higher the level of the injured vertebrae, the smaller the size of the retropulsed fragment needed compromise the neural tissues. We suggest that it is necessary to get enough decompression for restoration of spinal canal and recovery of neurological function and computed tomography was more sensitive than any other modality in detection the reduction of the retropulsed bony fragment into spinal canal.