A 71-year-old man presented with progressive dysuria. Several imaging examinations indicated possibility of prostate tumor, therefore he underwent prostate biopsy. This resulted in a diagnosis of granulocytic sarcoma of the prostate. Since bone marrow appeared normal on aspiration biopsy, he was treated with local irradiation. Prostate swelling then markedly diminished and his symptoms disappeared. However, four months later he progressed to AML. He then received systemic chemotherapy and achieved complete remission. We discuss the management of granulocytic sarcoma when findings do not indicate overt leukemia at the time of diagnosis.