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The diagnostic criteria for acute erythroid leukemia have been controversial since this disease was initially described. Using the current World Health Organization classification criteria, we retrospectively reviewed cases of acute myeloid leukemia or myelodysplastic syndrome in which erythroid precursors were >or=50% of the bone marrow nucleated cell population and the diagnosis of erythroleukemia was considered using older classification schemes. We collected 90 cases and separated them into four diagnostic groups: acute erythroid leukemia, erythroleukemia or erythroid/myeloid type (n=20); acute myeloid leukemia with myelodysplasia-related changes (n=22); therapy-related acute myeloid leukemia (n=32); and refractory anemia with excess blasts and preceding or concurrent history of erythropoietin therapy for anemia (n=16). Patients with acute erythroid leukemia were the youngest patient group and had the best overall survival. There was a statistically significant difference in overall survival between patients with acute erythroid leukemia versus acute myeloid leukemia with myelodysplasia-related changes (P=0.003) and between patients with acute erythroid leukemia versus therapy-related acute myeloid leukemia (P<0.0001). The presence of complex cytogenetic abnormalities (>3) was the only statistically significant independent variable that adversely affected survival in the acute erythroid leukemia group. Monosomy 5/del(5q) and monosomy 7/del(7q) were overrepresented in the context of complex chromosomal abnormalities. Our data suggest that acute erythroid leukemia, as currently defined in the World Health Organization classification, has become a rare disease. A majority of the cases reported previously as erythroleukemia are now classified as other entities. In addition, our data suggest that the current definition of acute erythroid leukemia, erythroleukemia type remains heterogeneous. One subset of acute erythroid leukemia patients has relatively low blast counts and are diploid. The prognosis of this patient subset is relatively good. The other subset has cytogenetic abnormalities similar to those in myelodysplastic syndromes and a poor prognosis.