Erythroblastic and/or megakaryocytic dysplasia (EMD) was evaluated in diagnostic bone marrow smears of 43 consecutively treated patients under 65 years with de novo acute myeloid leukemia (AML) M0-M5 according to FAB criteria. The evaluation was possible in 39 (91%) patients, i.e. in 32 of 34 patients with non-M3 AML treated in the study UHKT-911 and seven of nine cases with AML M3 treated in other studies. Among non-M3 AML 15 patients were categorized without EMD and 17 cases with EMD. Cytogenetic abnormalities of chromosome 5, 7, 3 or a complex karyotype were found in eight of 17 patients with EMD and in one of 15 cases without EMD (P = 0.018). Seven patients in each category exhibited a normal karyotype. Classical induction therapy with three to four doses of daunorubicin 45 mg/m2 and standard doses of cytosine arabinoside (AraC) for 7 days lead to complete remission in 11 of 14 (78.6%) cases without EMD but only in four of 14 (28.6%) cases with EMD (P = 0.021). High doses (2000 mg/m2 per 12-h x 10) of AraC plus daunorubicin induced complete remission in seven of 10 patients with EMD. Patients with EMD showed significantly worse overall survival (P = 0.03) with a median 13.5 months, while the median survival was estimated to 68.7 months in cases without EMD. The dysplastic features of EMD, karyotypes typical for myelodysplastic syndromes (MDS), poor response to classical therapy and survival show a relation of AML with EMD to MDS. AML without EMD may represent a different biological favorable category.