Chronic pediatric traumatic brain injury (TBI) is associated with significant and persistent neurobehavioral deficits. Using diffusion tensor imaging (DTI), we examined area, fractional anisotropy (FA), radial diffusion, and axial diffusion from six regions of the corpus callosum (CC) in 41 children and adolescents with TBI and 31 comparison children. Midsagittal cross-sectional area of the posterior body and isthmus was similar in younger children irrespective of injury status; however, increased area was evident in the older comparison children but was obviated in older children with TBI, suggesting arrested development. Similarly, age was correlated significantly with indices of tissue microstructure only for the comparison group. TBI was associated with significant reduction in FA and increased radial diffusivity in the posterior third of the CC and in the genu. The axial diffusivity did not differ by either age or group. Logistic regression analyses revealed that FA and radial diffusivity were equally sensitive to post-traumatic changes in 4 of 6 callosal regions; radial diffusivity was more sensitive for the rostral midbody and splenium. IQ, working memory, motor, and academic skills were correlated significantly with radial diffusion and/or FA from the isthmus and splenium only in the TBI group. Reduced size and microstructural changes in posterior callosal regions after TBI suggest arrested development, decreased organization, and disrupted myelination. Increased radial diffusivity was the most sensitive DTI-based surrogate marker of the extent of neuronal damage following TBI; FA was most strongly correlated with neuropsychological outcomes.