Now that the applications of positron emission tomography (PET) are becoming more clearly understood, PET is now being used in pediatric population. Important considerations in its use on children are patient preparation and radiation exposure. This issue reviews the use of PET to image children with Hodgkin and non-Hodgkin lymphoma, brain tumors, and inflammatory bowel disease, among other conditions. Also included is the use of PET to assess response to therapy.