We present the case of a 14-month-old male infant who underwent diffusion tensor imaging within 24 hours of traumatic brain injury. Although conventional MR findings that included those of diffusion-weighted imaging were unremarkable, full-tensor diffusion imaging revealed striking abnormalities in regions of brain that subsequently developed overt swelling. This case engenders important hypotheses regarding mechanisms of traumatic brain swelling and anisotropic diffusion of water in pathologic tissues.