Erythroleukemia is an uncommon leukemia with heterogeneous morphologic and karyotypic features. Some cases might actually represent acute myeloid leukemia with a reactive erythroid hyperplasia. In this report, we described a 68-year-old woman with erythroleukemia and monosomy 7 and showed by fluorescence in situ hybridization that both myeloid and erythroid lineage were clonally involved and that both normal and abnormal erythroid populations coexisted, albeit indistinguishable by morphological examination. These findings may account for the variation in the erythropoietic activity observed in the clinical course of erythroleukemia.