We report the muscle pathology in a 43-year-old woman who died of chronic graft versus host disease (GVHD) complicated by myositis and systemic transfusional hemosiderosis, after an allogeneic bone marrow transplantation and a donor leukocyte transfusion for acute myelogenous leukemia. Despite cyclosporin A treatment, fatal ventilatory failure progressed while she was still ambulant. Autopsy revealed the presence of chronic GVHD mildly involving the liver, skin, pericardium, pancreas, and salivary glands, in addition to skeletal muscles. Myopathic changes with mild inflammation and prominent iron deposition were found in the tibialis anterior muscle and, to a lesser degree, in the diaphragm and the intercostal muscle. There were iron deposits in both macrophages and sarcoplasm in the tibialis anterior. The iliopsoas and pectoralis major muscles showed prominent type 2 fiber atrophy; inflammation and iron deposition were minimal in the iliopsoas, but none in the pectoralis. Although we ascribed respiratory failure largely to GVHD myositis, weakness of the lower leg appeared to be aggravated by iron deposition superimposing the underlying GVHD myositis.