A 56-year-old female was diagnosed with acute myeloid leukemia (FAB: AML-M1). G-banding karyotype of her bone marrow showed complete tetraploidy (92, XXXX [24/24]). Although she achieved complete remission (CR) after induction therapy and maintained CR during consolidation therapy, relapse occurred only 2 months after discharge. When the relapse occurred, bone marrow karyotypic analysis showed complete tetraploidy again. The patient received reduced-intensity cord blood transplantation (RI-CBT), which induced CR for the second time. The patient is currently alive 24 months after transplantation and there have not been any signs of recurrence to date. There have been a few reports of AML with near-tetraploidy, but cases of AML with complete tetraploidy are extremely rare. Tetraploid AML has been reported to have a poor prognosis and there have been very few cases maintaining CR over the long term after chemotherapy alone. This is the first case of complete tetraploid AML successfully treated by RI-CBT. The clinical course of this case suggests that hematopoietic stem cell transplantation during the first CR phase should be considered a treatment option for tetraploid AML.