THE RELATIONSHIP BETWEEN the severity of the posttraumatic functional deficit and findings on magnetic resonance imaging (MRI) was investigated in a rat model of experimental spinal cord trauma. Thirty Sprague-Dawley rats were subjected to an identical, moderate, contusion injury of the spinal cord. Control animals underwent laminectomy without cord injury. The severity of the functional deficit was assessed with the Combined Behavioral Score (CBS). Animals were killed at 3, 7, 14, 21, or 28 days after injury, and the fixed, excised spinal cords were studied with MRI at 1.9 T. The lesion length was measured on sagittal spin-echo MRI. The lesion length measured on MRI was highly correlated with the CBS functional score (r= 0.56,P= 0.002). There were significant correlations between lesion length as determined by MRI and by histological morphometry (r= 0.44,P= 0.02), between histological morphometric lesion length and CBS functional deficit (r= 0.76,P< 0.001), and between the area of residual white matter at the lesion epicenter, determined by histological techniques, and the severity of functional deficit (r= −0.59,P= 0.001). A qualitative estimate of the area of preserved white matter, derived from MRI, was significantly correlated with the severity of functional deficit (r= −0.56,P= 0.006). A multiple regression of MRI-determined lesion length and MRI estimate of residual white matter versus CBS explained more than 42% of the variability of the functional deficit among these animals subjected to the same weight drop injury. We conclude that MRI parameters are reliable predictors of the severity of neurological deficit in experimental spinal cord trauma.