Erythroleukemia is a heterogeneous disorder that can have an excess of myeloblasts or proerythroblasts in the setting of dyserythropoiesis. The French-American-British classification, established in 1976 and subsequently revised, allows only for the diagnosis of erythroleukemias whose immature elements are predominated by myeloid blasts, previously described as DiGuglielmo's syndrome. However, there is another form of erythroleukemia, in which the predominant immature elements are proerythroblasts, called DiGuglielmo's disease. To clarify this issue, 23 cases of erythroleukemia were reviewed and classified: 10 with a myeloblast predominance and 13 with a proerythroblastic predominance. These two forms of erythroleukemia can be distinguished on the basis of quantitative and qualitative morphologic features. When there were 30% or more proerythroblasts, calculated by dividing the total erythroid component into the proerythroblasts, there were few to no myeloblasts, no Auer rods, and increased cytoplasmic vacuoles; and myeloperoxidase staining was negative. The malignant proerythroblasts had increased block and blush periodic acid-Schiff positivity. The most frequent chromosomal abnormalities involved chromosomes 5 and 7. The patients with DiGuglielmo's disease had a median survival time of 2 months (range, 0.06 to 9 months), compared to a median of 16 months (range, 2 to 48 months), in patients with DiGuglielmo's syndrome. The erythroleukemia with the preponderance of proerythroblasts had a worse prognosis because many of the individuals did not survive long enough to respond to the therapy initiated. Erythroleukemia with 30% or more proerythroblasts should be included in the French-American-British classification because it behaves clinically and appears morphologically as an acute leukemia rather than a myelodysplastic syndrome.