This article is a brief review on the physics of diffusion imaging as well as the pertinent adult literature regarding stroke and diffusion imaging. The remainder of the article focuses on the potential uses of diffusion imaging for the evaluation of hypoxic ischemia injury in pediatric populations. In particular, diffusion changes in hypoxic ischemia injury in newborns are reviewed as the diffusion abnormalities in immature brain may behave in a manner different from adults.