Abstract No diffusion tensor imaging (DTI) study has yet investigated ataxia in diffuse axonal injury (DAI). In the current study, we used DTI to investigate cerebellar peduncle lesions of patients who showed severe ataxia following DAI. Six patients with severe ataxia following DAI and six age-and sex-matched control subjects were recruited. DTIs were acquired using a sensitivity-encoding head coil on a 1.5 T system. Using DTI-Studio software, three cerebellar peduncles (superior cerebellar peduncle, SCP; middle cerebellar peduncle, MCP; inferior cerebellar peduncle, ICP) were evaluated. In each cerebellar peduncle, fractional anisotropy was estimated using the regions of interest method. We defined a lesion as a fractional anisotropy value two standard deviations below that of normal controls. All six patients had an average of 6.3 lesions (range 3–12). Twenty of 36 total cerebellar peduncles revealed more than one lesion (SCP: 8, ICP: 7, MCP: 5). In each of the 20 cerebellar peduncles, all the lesions displaying the lowest FA values relative to that of normal controls (11 peduncles; 55%) were located in the junction between brain stem and cerebellum and post-junctional area (nine peduncles; 45%). The junction and peri-junctional areas between the brain stem and cerebellum appear to be the most vulnerable area by DAI, with the order of incidence SCP, ICP, and MCP. Evaluation of the cerebellar peduncles using DTI can be helpful in patients with ataxia following DAI.