Acute promyelocytic leukemia (APL) is characterized by a serious hemorrhagic syndrome, unique morphologic findings, and its response to retinoids. Tetraploidy is a very rare chromosomal abnormality in acute myelocytic leukemia. This report presents a unique case of APL with a tetraploid clone characterized by two t(15;17) without other chromosomal changes, as well as PML/RARA rearrangements confirmed fluorescence in situ hybridization. The morphology of the blast cells was that of the classic M3 subtype, but the mean blast size exceeded that of control APL cases with diploidy. A chromosomal study revealed a 92,XXXX,t(15;17)(q22;q21)x2 karyotype in all 20 metaphase spreads. Despite all-trans-retinoic acid (ATRA) treatment and chemotherapy, leukemic cells persisted in the blood, and the patient died of an intracranial hemorrhage on the 16th day after admission.