Graft-versus-host disease (GVHD) is a T cell-mediated disease seen most commonly after hematopoietic stem cell transplantation. Rarely, a GVHD-like disease can be seen in patients with malignant thymoma. We describe a 50-year-old man with malignant thymoma who developed skin, liver, and intestinal manifestations similar to that seen in GVHD. We also review other reported cases of GVHD-like manifestations in the setting of thymoma and propose "thymoma-associated multiorgan autoimmunity" as a name for this novel disease. Specifically, thymoma-associated multiorgan autoimmunity is defined as a disease of the liver, intestine, or skin, which on histopathology resembles GVHD but is seen in the setting of malignant thymoma and not after hematopoietic stem cell transplantation.