Myeloid/NK cell precursor lymphoma/leukemia has been suggested to be of precursor NK origin. We report a 1-year-old boy with myeloid/NK cell precursor lymphoma/leukemia who presented with a skin nodule. Biopsy of the skin nodule specimen revealed CD45(+), CD56(+), myeloid antigen(+), CD7(-), CD3(-), CD19(-), CD34(-), CD4(-) by flow cytometry and myeloperoxidase (MPO)(+), TdT(+), cytoplasmic CD3(+) by immunohistochemistry. He received acute myeloid leukemia-oriented combination chemotherapy. Although his skin nodule disappeared, regrowth was observed; a biopsy was performed again, showing that the immunophenotype was CD56(+), myeloid antigen(+), HLA-DR(+), MPO(-), CD3(+) and TCRgammadelta(+). Being refractory to chemotherapy, he underwent stem cell transplantation from his father. However, he relapsed again and died from septic shock. Although myeloid/NK cell precursor acute leukemia is characterized by CD7(+), CD56(+), CD3(-), CD34(+) and myeloid antigen(+) phenotype, the blast cells of our patients lacked CD34 and CD7 expression while expressing myeloid antigens. Furthermore, CD94 1A transcripts were predominantly expressed rather than CD94 1B, implying their origin in immature NK cells. After acute myeloid leukemia-oriented combination chemotherapy, his blasts acquired stable CD3 expression and TCRgammadelta rearrangement at recurrence. The blast cells possessed features overlapping both myeloid/NK precursor acute leukemia and blastic NK/precursor acute lymphoma/leukemia. These observations suggest that two subclones originated from common precursors.