Diffuse axonal injury (DAI) is identified as one of the most important causes of cognitive disorders in patients with traumatic brain injury. Radiologic recognition of DAI can help in understanding the clinical syndrome and in making treatment decisions. However, CT and conventional MRI are often normal or demonstrate lesions that are poorly related to the cognitive disorders present. Recently, diffusion tensor imaging (DTI) and fiber tractography (FT) have been shown to be useful in detecting various types of white matter damage. The aim of this study was to evaluate the feasibility of using DTI and FT to detect lesions in DAI patients, and to correlate these DAI lesions with the patients' cognitive disorders. We investigated 9 normal volunteers and 9 patients with DAI. The DAI patients had impaired intelligence, as well as attention, memory and executive function disorders that restricted their activities of daily living. In the DAI patients, DTI showed abnormal brain areas in the corpus callosum, fornix, frontal and parietal lobe white matter, and FT revealed interruptions of the white matter fibers in the corpus callosum and the fornix when compared with the normal volunteers, while no lesions were found on conventional MRI. DTI and FT can directly visualize DAI lesions, which cannot be reliably detected by conventional methods. Accordingly, both DTI and FT may be useful techniques for the evaluation of DAI, and may have the potential to be applied to planning rehabilitation therapy, and predicting the neurologic prognosis in DAI patients with cognitive disorders.