This review discusses aplastic anemia (AA), paroxysmal nocturnal hemoglobinuria (PNH) and the myelodysplastic syndrome (MDS, all diseases associated with severe anemia. Anemia in AA and MDS is mainly due to defective or lacking eryhtropoiesis in the case of PNH mostly due to hemolysis. Management by transfusions, the use of growth factors and iron chelation is being discussed as are more specific treatment approaches directed against the underlying disease.