Myeloid sarcoma (MS) is a solid extramedullary tumor that is composed of immature myeloid cells. The incidence of MS in patients with acute myeloid leukemia (AML) has been reported to be 3∼8%. Lymph nodes are the most frequent site of presentation for MS, and other clinical presentations such as an abdominal mass with bowel involvement, a pancreatic mass, isolated central nervous system infiltration, a testicular mass and breast lumps have also been reported. AML with mediastinal MS is a relatively rare disease. The patients with AML with mediastinal MS has been reported to have complex cytogenetic abnormalities and a poor long-term prognosis. The optimal treatment of AML with MS remains to be determined. We report here on an unusual case of a 37-year-old man who presented multiple lymph node enlargements on the neck and a huge mediastinal mass that was considered to be lymphoma. He was finally diagnosed as AML with MS according to the surgical excisional biopsy of a left supraclavicular lymph node and bone marrow examination. He achieved complete remission and the multiple enlarged lymph nodes on the neck and the mediastinal mass disappeared after remission induction chemotherapy. Thereafter, he received HLA-matched unrelated allogenic hematopoietic stem cell transplantation.