Disruption of the cytoskeletal network and axonal membranes characterizes diffuse axonal injury (DAI) after traumatic brain injury. Histologic abnormalities seen in DAI hypothetically decrease the diffusion along axons and increase the diffusion in directions perpendicular to them. We tested this hypothesis by measuring the diffusion characteristics of traumatized brain tissue with use of diffusion tensor imaging (DTI). Two patients with traumatic brain injuries and five control subjects were studied with DTI. Mechanisms of change in fractional anisotropy maps of DTI were explored using an eigenvalue analysis of the diffusion tensor. Axial diffusivity (λ1) were decreased and radial diffusivity ((λ2+λ3)/2) were increased in both caudal middle frontal gyri, pars orbitalis gyri, fusiform gyri, parahippocampal gyri (patient 1), caudal middle frontal gyri, precentral gyri, middle temporal gyri (patient 2). Both axial and radial diffusivity were increased in most of the frontal lobe gyri. We applied new analytic methods for DAI in traumatic brain injury.