The authors present a review of some sub-units of MDS with a specific clinical and laboratory characteristic. The myelodysplastic syndrome (MDS) must be divided into sub-types either according to FAB or WHO classification. When establishing the diagnosis it is important to state whether primary or secondary MDS is involved. Nowadays we can however define the diagnosis of MDS more accurately by assessing further sub-units which have their clinicalpicture,prognosisandlaboratory finding.These sub-units are divided into three groups: 1. mixed syndromes which comprise hypoplastic MDS and mixed MDS-MPS, 2. cases with a specific histological or morphological picture, i.e. MDS with myelofibrosis, MDSwith eosinophilia,MDS with aggregation of granulocyte chromatin, two forms of sideroblastic anaemia where we can add also idiopathic macrocytosis and finally 3. cases with specific cytogenetic findings such as the 5q minus, syndrome monosomy 7 in children, pathology of chromosome 17 (17p-, isol17q) and some less frequent chromosomal aberrations. Knowledge of these sub-units will help us to establish the prognosis of the disease and thus also therapy decision.

        Key words: MDS diferentiation, overlap syndromes, morphological aberrations, fibrousis, cytogenetic sub-units