Microsatellite instability (MSI) and p53 alterations which may represent major mechanisms of genetic instability, are rarely observed in de novo acute myeloid leukemia (AML) but may play a substantial role in subgroups characterized by either a myelodysplastic prephase (sAML), previous chemotherapy (tAML) or a complex aberrant karyotype. We performed allelotyping and p53 mutation analysis in 75 patients with morphologically and cytogenetically classified AML.