Myelodysplastic syndromes (MDS) are clonal disorders of pluripotent hematopoietic stem cells. MDS occur predominantly over the age of 60 years. The diagnosis of MDS is based on the examination of both blood films and bone marrow aspirate. Diseases such as vitamin B12 and/or folate deficiency, or cytotoxic therapy leading to a marrow dysplasia should be ruled out. Five subtypes are described in the FAB classification : refractory anaemia or refractory cytopenia, refractory sideroblastic anaemia, refractory anaemia with excess of blasts, refractory anaemia with excess of blasts in transformation, chronic myelomonocytic leukaemia. This FAB classification is based on a small number of parameters: percentage of blood and marrow blasts, percentage of ringed sideroblasts and blood monocytes. The anaemia is typically normo- or macrocytic, non regenerative, and in half cases is associated with neutropenia and/or thrombocytopenia. During blood film examination, cell abnormalities have to be notified, i.e. anisocytosis, poikilocytosis of red cells, morphological abnormalities of neutrophils including hypogranulation, hypolobulation, abnormal large platelets. The prognostic and the treatment of MDS depend on the subtype of the FAB classification, the patient's age, the percentage of marrow blasts, the importance of cytopenia, the presence or not of cytogenetic abnormalities and the existence or not of HLA-identical donor.