Tetrasomy 8 is an extremely rare chromosome abnormality, one that has been reported in only a few cases with myeloid malignancies. The majority of reported cases consist of acute myelogenous leukemias (AML) of monocytic lineage. In slightly more than half of the patients, tetrasomy 8 was the single cytogenetic abnormality. Fluorescence in situ hybridization revealed tetrasomy 8 and trisomy 8 concurrently in all but one of the bone marrow samples. The clonal relationship between trisomy 8 and tetrasomy 8 in these cases remains to be clarified. Patients with tetrasomy 8 have a poor prognosis, and only 1 out of 33 patients was free of disease 3 years after autologous bone marrow transplantation. Here, we report the case of a 25-year-old female patient with monocytic leukemia and tetrasomy 8.