Cerebral concussion and mild traumatic brain injury (TBI) have been used interchangeably, although the two terms have different definitions. Traumatic axonal injury (TAI) is a more severe subtype of TBI than concussion or mild TBI. Regarding the evidence of TAI lesions in patients with concussion or mild TBI, since the 1960’s, several studies have reported on TAI in patients with concussion who showed no radiological evidence of brain injury by autopsy. However, conventional CT and MRI are not sensitive to detection of axonal injury in concussion or mild TBI, therefore, previously, diagnosis of TAI in live patients with concussion or mild TBI could not be demonstrated. With the development of diffusion tensor imaging (DTI) in the 1990’s, in 2002, Arfanakis et al. reported on TAI lesions in live patients with mild TBI using DTI for the first time. Subsequently, hundreds of studies have demonstrated the usefulness of DTI in detection of TAI and TAI lesions in patients with concussion or mild TBI. In Korea, the term “TAI” has rarely been used in the clinical field while diffuse axonal injury and concussion have been widely used. Rare use of TAI in Korea appeared to be related to slow development of DTI analysis techniques in Korea. Therefore, we think that use of DTI analysis techniques for diagnosis of TAI should be facilitated in Korea.