Graft versus host disease (GVHD) is one of the major causes of death in patients undergoing allogeneic hematopoietic cell transplantation. 18F-FDG PET/CT (2-[fluorine-18] fluoro-2-deoxy-D-glucose, Positron emission tomography- CT) is a noninvasive technique that allows quantifying and precisely localizing 18F-FDG uptake in the entire body. 18F-FDG uptake is caused by increased local metabolic activity. In this study, we aim to evaluate and characterize the correlation between CT-PET findings in patients suspected to have acute GVHD, and the disease course.