Elderly patients with secondary acute myeloid leukemia (AML) following myelodysplastic syndrome (MDS) are often medically unfit for or resistant to chemotherapy, and their prognosis is dismal. In the present paper, we reported a case of secondary leukemia following MDS in an 80-year-old male patient who was deemed unfit for chemotherapy owing to his old age and poor physical condition. Despite a high tumor burden, treatment with AZA exerted a remarkable response, leading to an immediate cytoreduction in our case. Our results suggest that AZA can be an attractive therapeutic option for elderly MDS or AML patients, offering adequate efficacy and high tolerability. © 2014 Takahiro Kumode et al.