The MDS represents a heterogeneous group of clonal disorders of pluripotent hematopoietic stem cells characterized by hypercellular bone marrow, with dysplastic changes in multiple cell lineages, ineffective hematopoiesis leading to peripheral blood cytopenia. Acute myelogenous leukemia (AML) is a malignancy originating in a multipotential hematopoietic cell characterized by clonal proliferation of abnormal blast cells in the marrow and impaired production of normal cells, resulting in anemia and thrombocytopenia. Cytogenetic similarities were noted between AML and MDS, suggesting common etiopathogenetic mechanism. We have studied, by conventional cytogenetics & fluorescence in situ hybrielization (FISH) chromosome 5 in a series of 34 patients diagnosed as MDS (12 patients) / AML 22 (patients) according to WHO & FAB criteria. The deletion of long arm of chromosome 5 (5q-) are one of the most common structural abnormalities observed in MDS and AML. Band 5q31 is invariably lost and has been designated a critical region. It is proposed that an AML/MDS leukemia suppressor gene residues an 5q31. Only by FISH techniques one case of MDS (8.3%) as well as one case of AML (4.5%) were found to have 5q deletion.FISH allowed the identification of small deletions, which was totally unidentified by classical cytogentic. This show the superiorty of FISH over conventional cytogemetics.