Dermatologists are not so familiar with transplantation immunity, especially graft-versus-host disease (GVHD). In order to understand GVHD, GVHD and other related diseases are discussed. The clinical course of bone marrow transplantation and GVHD are explained. GVHD is classified into congenital, iatrogenic or unknown GVHD with its origin. GVHD is also classified into hyperacute, acute or chronic GVHD with the time of onset. Pseudo GVHD (GVHD-like disease) appears following autologous transplant or syngeneic bone marrow transplantation. Postoperative erythema and post-transfusion GVHD are GVHD-related diseases and are also described.