A 56-year-old woman was brought to the emergency room with gum swelling and pain. Biopsy of the gingiva revealed sheet-like proliferation of myeloperoxidase and CD45-positive large cells, and she was diagnosed with granulocytic sarcoma. Two years later, bone marrow involvement of granulocytic sarcoma was suspected. Her chromosome study repeatedly revealed a 46,XX,t(5;12)(q13;p13) karyotype. Case reports of t(5;12)(q13;p13) are extremely rare in the literature. To our knowledge, this is the first report of t(5;12)(q13;p13) in a patient with acute myelogenous leukemia with preceding granulocytic sarcoma.