Traumatic brain injury (TBI) is the most common cause of death and disability in young people. The functional outcome in patients with TBI cannot be explained by focal pathology alone, and diffuse axonal injury (DAI) is considered a major contributor to the neurocognitive deficits experienced by this group. The aim of the present study was to investigate whether diffusion tensor imaging (DTI) offers additional information as to the extent of damage not visualized with standard magnetic resonance imaging (MRI) in patients with severe TBI. Nine chronic male TBI patients and 11 matched healthy controls were recruited. Results of the voxel-based analysis of fractional anisotropy (FA) maps and apparent diffusion coefficient (ADC) maps revealed significant differences in anisotropy in major white matter tracts, including the corpus callosum (CC), internal and external capsule, superior and inferior longitudinal fascicles, and the fornix in the TBI group. The FA and ADC measurements offered superior sensitivity compared to conventional MRI diagnosis of DAI. Region-of-interest (ROI) analyses confirmed these results in the investigated regions. The findings of this study support the hypothesis that severe TBI is accompanied by DAI. The DTI changes were more prominent on the right side that contained the focal pathology in most of the patients and accurately reflected differences in both hemispheres. In conclusion, DTI holds great promise as a diagnostic tool to identify and quantify the degree of white matter injury in TBI patients.