Diffusion tensor tractography (DTT) is useful for elucidating the status of the corticospinal tract (CST). The purpose of this study was to investigate the usefulness of DTT for determining the causes of motor weakness in patients with traumatic brain injury (TBI). Five patients with TBI were recruited for this study. DTT was performed using 1.5-T with a Synergy-L Sensitivity Encoding (SENSE) head coil. DTT was obtained with termination criteria of FA < 0.2 and an angle change > 45 degrees . On the DTT of patient 1, who had diffuse axonal injury, the focal lesion was detected in the left pons, and was not detected on routine brain images. In patients with deep cerebral hemorrhage, the integrity of the CST of patient 3 was preserved, although the lesion was more extensive than that of patient 2, who showed severe degeneration with the disruption of the CST at the lesion site. In patient 4, the integrity of the left CST was disrupted by a left transtentorial herniation. Although the CST of the affected hemisphere was connected at the cortex level in patient 5, who had a cortical contusional hemorrhage, the motor function of the lower extremity was worse than that of the upper extremity according to the involvement of the somatotopic area of the primary motor cortex. DTT would be useful in elucidating the causes of motor weakness in patients with TBI at the subcortical level, including conditions such as diffuse axonal injury, deep intracerebral hemorrhage, and transtentorial herniation.