Abstract Erythroleukemia (EL) is a rare form of myelogenous leukemia the classification and definition of which has evolved over the course of its 80-year descriptive history. In 1976 the French American British (FAB) Cooperative Group included EL within the classification system of acute myelogenous leukemias as AML-M6, and agreed on a quantitative standard to be used in the diagnosis of this disorder. The standards were revised in 1985 to the form in use today. We selected a series of 15 cases from our records which specifically fit the FAB criteria for AML-M6. Extensive direct comparison between our series and the old literature is not practical because of the changes which have occurred in classification and definition of the disease. Overall we found a rough correlation between the clinical and laboratory data shown in the old literature on EL and data from our cases. These cases underscore characteristic laboratory features which correspond to what is now defined as AML-M6: these patients present with pancytopenia, frequent peripheral blood nRBCs and no, or few, peripheral blood blasts. In addition, we note the presence of a hybrid myeloid-erythroid blast in the bone marrow in this disease and suggest that this may be characteristic of this type of AML. Old literature on EL has generally shown it to be a disease of the elderly, yet we found a subset of younger patients whose clinical outcome was significantly better than that of the older patients. Finally, EL has historically been viewed as a disease in which patients progress from a prodrome through erythroleukemia to other acute myeloid leukemia (AML) subtypes. Consistent with this idea, half of our 15 patients had been previously diagnosed with myelodysplastic syndrome or received chemotherapy. On the other hand only one of the 15 patients converted to another type of AML during his course.