STUDY DESIGN A retrospective, consecutive case series. OBJECTIVE To determine the risk factors that have a significant correlation with the severity of neurologic impairment in thoracolumbar and lumbar burst fractures. SUMMARY OF BACKGROUND DATA The correlation between spinal canal stenosis due to bony fragments and the severity of neurologic deficits in thoracolumbar and lumbar burst fractures remains controversial. Moreover, there have so far been no reports in the literature in which the risk factors (spinal canal stenosis and the disruption of posterior ligamentous complex) causing a severe neurologic deficit were analyzed using a multiple logistic regression model. METHODS A review of the clinical data (neurologic impairments on admission and a finding of posterior ligamentous complex disruption at the time of operation), axial computed tomography, and plain lateral radiography of 216 patients in thoracolumbar (T11-L1) and lumbar (L2-L5) burst fractures was performed. The factors related to neurologic impairments were analyzed using a multiple logistic regression model. RESULTS In all cases, both the spinal canal stenosis (P < 0.01) and disruption of posterior ligamentous complex (P < 0.01) were significant risk factors. Interestingly, these two risk factors varied according to the injury levels: at thoracic level, the spinal canal stenosis (P < 0.01); at the first lumbar spine, the disruption of the posterior ligamentous complex (P < 0.01); and at the lumbar spine below L2, both of the spinal canal stenosis (P < 0.01) and the disruption of posterior ligamentous complex (P < 0.05) were significant risk factors, respectively. CONCLUSION In the patients with thoracolumbar and lumbar burst fractures, the significance of the two important risk factors related to clinical results, namely, the stenosis ratio of spinal canal and the disruption of posterior ligamentous complex, were found to vary depending on the level of injury.