A 75-year-old female patient presented with late relapse of acute myeloid leukemia (AML). She received a single cycle of azacitidine before refusing further treatment. Around 6 weeks after this single azacitidine cycle, complete remission—according to international working group criteria—was observed with continuous improvement in peripheral blood counts to normal values, transfusion-independence, normal blast count (< 5 %) with normal morphology and flow cytometry, as well as a normal bone marrow karyotype and no dysplastic stigmata suggestive of a coexisting myelodysplastic syndrome. The patient also showed a pronounced improvement in performance status. Seven months later a second relapse occurred, followed by one additional azacitidine cycle that showed only a transient and a minor increase in thrombocytes and granulocytes, corresponding to an international working group nonresponse. As azacitidine treatment was interrupted after a single cycle, this case gives insight into the kinetics of response. The lack of response to azacitidine in AML after the second relapse suggests that azacitidine administration should be maintained after response.