De novo acute myeloid leukemias (AML) patients with normal cytogenetics represent a standard risk cytogenetic group. Erythroblastic and/or megakaryocytic dysplasia (EMD) in diagnostic bone marrow smears of 28 consecutive AML patients with a normal karyotype was studied. Twelve patients 21-85 (median 48) years old were categorized without EMD, 14 patients 34-90 (median 58) years old with EMD, and 2 patients were not evaluable for EMD. One cycle of induction therapy 4 + 7, with 4 doses of daunorubicin 45 mg/m2/d and standard doses of cytosine arabinoside for 7 days induced 10 complete and 2 partial remissions in 12 cases without EMD but lead to only one complete remission, 6 non-responses and 3 induction deaths in 10 cases with EMD (p = 0.002). However, high doses of cytosine arabinoside plus daunorubicin induced complete remission in 6 of 7 patients with EMD. In patients under 66 years treated by intensive consolidations the estimate of median survival was 50.6 months in 10 cases without EMD, significantly higher than 8.0 months in 11 cases with EMD (p = 0.043). De novo AML with normal cytogenetics might be divided into two biological categories, the first favorable-risk category without EMD and the second poor-risk category with EMD.