The purpose of the present study is to identify otherwise occult white matter abnormalities in patients suffering persistent cognitive impairment due to mild traumatic brain injury (TBI). The study had Institutional Review Board (IRB) approval, included informed consent and complied with the U.S. Health Insurance Portability and Accountability Act (HIPAA) of 1996. We retrospectively analyzed diffusion tensor MRI (DTI) of 17 patients (nine women, eight men; age range 26-70 years) who had cognitive impairment due to mild TBI that occurred 8 months to 3 years prior to imaging. Comparison was made to 10 healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) images derived from DTI (1.5 T; 25 directions; b = 1000) were compared using whole brain histogram and voxel-wise analyses. Histograms of white matter FA show an overall shift toward lower FA in patients. Areas of significantly decreased FA (p < 0.005) were found in the subject group in corpus callosum, subcortical white matter, and internal capsules bilaterally. Co-located elevation of mean diffusivity (MD) was found in the patients within each region. Similar, though less extensive, findings were demonstrated in each individual patient. Multiple foci of low white matter FA and high MD are present in cognitively impaired mild TBI patients, with a distribution that conforms to that of diffuse axonal injury. Evaluation of single subjects also reveals foci of low FA, suggesting that DTI may ultimately be useful for clinical evaluation of individual patients.