Cerebral CT scanning is routine in the acute evaluation of traumatic brain injury (TBI) patients. MRI has been reported to identify cerebral lesions better than CT scan. The purpose of this study was to determine whether MRI influenced the acute diagnosis and management of TBI patients. A retrospective medical records review was performed on all TBI patients undergoing cerebral CT scan and MRI admitted to a regional trauma center during a 2-year period. Patient data collected included demography, extent of TBI, CT scan and MRI use, and therapeutic interventions. Forty TBI patients (initial Glascow Coma Scale, 8.8+/-0.7) underwent 79 CT scans and 40 MRIs. Time to initial CT scan was 6.3+/-4.3 hours and time to MRI was 2.9+/-3.1 days. Nine patients (22.5%) had injuries on CT scan but not on MRI, most commonly skull fractures or small subarachnoid hemorrhages. Twenty-four patients (60%) had injuries on MRI but not on CT scan, most commonly corpus callosum shear injuries. There were two cases of child abuse and both had injuries of varying ages identified by MRI, but not CT. All injuries requiring a therapeutic intervention or change in management were identified by CT scan. Magnetic resonance angiography identified one patient with a traumatic internal carotid artery thrombosis. The performance of MRI resulted in additional charges of $75,640 or $3,152/patient identified with a new lesion. Although MRI identifies lesions not evident on CT scan, MRI does not alter management plans and is of limited value in the acute management of TBI. MRI may be of medicolegal benefit in cases of child abuse.