Graft-versus-host disease (GVHD) classically involves the skin, intestines, liver, esophagus, and tongue. clinically apparent disease involving the heart, lungs, kidneys, and central nervous system (CNS) is frequently secondary to other complicating factors. This report describes a case of an infant with severe combined immune deficiency (SCID) who developed unusual manifestations of GVHD following a bone marrow transplant (BMT). These were complete heart block and respiratory insufficiency in the absence of significant pulmonary disease. He lived 133 days post-transplantation. At autopsy, the brain showed focal lymphohistiocytic aggregates which may represent a hitherto unreported lesion of GVHD.