A case of acute myelomonocytic leukemia in a 74-year-old male patient is described whose bone marrow cells had a normal male karyotype but with double minutes chromosomes (DM). The patient had no history of exposure to mutagenic or carcinogenic agents, or a history of other malignancies. The clinical and etiologic implications of DM as a sole karyotypic anomaly in the leukemic cells are discussed.