Two patients with "de novo" ANLL and tetrasomy of chromosome 8 at diagnosis are described. A mosaic karyotype with coexistence of normal metaphases was found in both cases. Trisomy 8 was also present in one metaphase of the first patient. Fluorescent in situ hybridization with a centromeric probe from chromosome 8 was applied in the second case, confirming the presence of a minor population with trisomy 8 in interphase nuclei.