The use of hematopoietic stem cell transplantation (HSCT) in the treatment of children afflicted with many potentially fatal malignant and nonmalignant diseases is well recog-nized. Although outcomes continue to improve and the utility of HSCT is increasing, HSCT remains a complicated process necessitating support from many medical disci-plines, including radiology. Importantly, children who un-dergo HSCT are at risk for the development of specific complications that are linked to the timeline of transplan-tation, as well as to the relationship between the underly-ing diagnoses, severe immune deficiency, cytoreductive regimen, and graft-versus-host reactions. An understand-ing of the complex interplay of the immune status, thera-peutic regimen, and disease allows increased diagnostic accuracy. Successful treatment of these high-risk children requires that radiologists who are involved with their care be familiar with broad concepts, as well as with specific problems that frequently occur following HSCT. In this article, the clinical aspects of pediatric HSCT are summa-rized, including common complications, and imaging fea-tures of these complications are described.