Presence of donor lymphocytes in the recipient blood circulation early after solid organ transplantation (SOT) is not uncommon, and it may play a role in organ tolerance. However, persistence of donor lymphocytes in association with evidence of engraftment in organs such as skin, gastrointestinal tract, liver, and bone marrow are the principal features of graft-vs-host-disease (GVHD). Although GVHD is a common complication after allogeneic hematopoietic stem cell transplantation (HSCT), it is rare after SOT, likely due to a markedly lower donor lymphocyte burden associated with SOT compared with HSCT. In keeping with this theory, GVHD is more common after transplantation of organs with greater amounts of lymphoid tissue such as the liver and small bowel compared with the kidney, heart, and lung. To date, only four other cases of GVHD after lung transplantation, and six cases after heart/lung transplantation, have been reported.