BACKGROUND Here we report 2 rare cases of acute myeloid leukemia (AML) complicated with hemolytic anemia limited to the myelodysplastic syndrome (MDS) stage, and disappearing in leukemic transformation. METHODS/RESULTS A 66-year-old man with MDS-RAEB-2 was admitted to hospital for severe anemia with increased reticulocyte counts. Hemolytic anemia was suspected, and it was ameliorated by methylprednisolone pulse therapy. Although anemia grew worse when steroids were tapered off, later improvement coincided with an increase in myeloblasts in the peripheral blood, i.e. with leukemic transformation. In another case, a 68-year-old man was admitted to hospital when laboratory findings showed a white blood cell count of 24,800/microl with increased myeloblasts (62.5%), leading to the diagnosis of AML with multilineage dysplasia. Following a decrease in blasts due to anti-cancer drugs, supporting the MDS-RAEB-2 status, severe anemia with increased reticulocytes and positive direct antiglobulin test was diagnosed, suggesting the existence of autoimmune hemolytic anemia, which was then ameliorated by steroid therapy. CONCLUSIONS The simultaneous loss of autoimmunity and leukemic cell expansion observed in our cases may possibly suggest a common underlying mechanism.