A 34 year old man presented with a rash on the arms, legs and back which had appeared one month earlier, and fever (38 ^oC) of ten days’ duration, associated with fatigue and weakness. Local antihistamine and corticosteroid preparations were not beneficial, while the administration of cefaclor had no effect on the fever. His past medical history was unremarkable. Physical examination revealed pallor, mild hepatomegaly (2 cm below the costal margin) and violaceous, raised, non-tender cutaneous lesions, with a maximum diameter of 3 cm, located on the back, and the upper and lower extremities (fig.1). Hematological examination showed: Ht: 26.5%, Hb: 8.7 g/dL, reticulocytes 17x10⁹/L, white blood cells 3.2x10⁹/L (neutrophils 16%, lymphocytes 32%, monocytes 9% and blasts 43%), platelets 62x10⁹/L. On the blood smear the blasts appeared large with bilobed cerebriform nuclei, delicate lacy nuclear chromatin, prominent/large nucleoli and agranular basophilic cytoplasm (fig.2). The biochemical profile showed an increase of lactate dehydrogenase (758 IU/L) and hyperuricemia (8.7 mg/dL). The bone marrow aspirate was hypercellular and 60% infiltrated by blasts morphologically similar to those in the blood smear. The cytochemical stains showed weakly positive, peroxidase and PAS reaction, while the reaction for nonspecific esterase with α-naphthyl acetate was strongly positive and the reaction for naphthol AS-D chloracetate was negative. Blast immunophenotyping was positive for HLA-DR, CD13, CD14, CD33 and CD45. Karyotype analysis revealed a t(9;11) (p22;q23) translocation.