A case of a 37-year-old woman presenting with acute agnogenic myeloid metaplasia (AAMM) is described. The disease had a stormy course and was characterized by moderate splenomegaly, persistently depressed WBC counts, extramedullary hemopoiesis and presence of a high percentage of atypical myeloblasts in the peripheral smear. Platelets were persistently low, reticulocytes significantly below normal, notwithstanding anemia. Hct tended to fall progressively to intolerably low values in the absence of transfusion.The chromosomal mapping of peripheral blood revealed the presence of a trisomy of chromosome No. 8. This abnormality already demonstrated in two previous cases of acute myelofibrosis and the clinical course of the disease suggest that acute myelofibrosis and AAMM could be the same disease while chronic myelofibrosis should be considered a separate entity. Also, it is possible that AAMM with trisomy of chromosome No. 8 and stormy clinical course may be a different entity from the acute myeloproliferative disorders associated with other chromosomal abnormalities.