We report a case in which an aflatoxin-producing strain of Aspergillus flavus (A. flavus) caused systemic aspergillosis in a post-transplant 41-year-old man with acute myeloid leukemia. The leukemia was initially resistant to two courses of induction chemotherapy. The third course of chemotherapy, however, induced complete remission. Thereafter, the patient underwent bone marrow transplantation from his HLA identical brother. Pulmonary aspergillosis was suspected as a complication during induction chemotherapy. Twenty days after the transplant, the patient's absolute neutrophil count had increased to 500/microliter. However, the symptoms of pulmonary aspergillosis were aggravated following neutrophil and monocyte recovery. The patient died of sinus arrest due to complete atrioventricular block 31 days after his transplant. At autopsy, we found that the fungus had invaded the brain, lungs, spleen, kidneys, skin, and myocardium, including the sinoatrial conduction system. There was no sign of acute graft-versus-host disease. A strain of A. flavus was isolated from cultured tissue samples of fungal lesions and shown by thin-layer chromatography to produce aflatoxins. To our knowledge, this is the first case report describing an infection by an aflatoxin-producing A. flavus.