Cytogenetics is science about structure, function and chromosome evolution. Cytogenetics is also involved in the study of behavior of chromosomes during division of somatic and germ cells. Clinical cytogenetics is following structural and numerical chromosomal changes which can be either inborn i.e. constitutional or acquired. Acquired chromosomal changes are present in malignant tumors. Cytogenetic examination is recommended in patients with birth defects, in prenatal diagnostics, in cases of assisted reproduction to determine chromosomal complement of foetus etc. In oncocytogenetic laboratories specific and non- -specific chromosomal rearrangements are studied and their determination is improving diagnostic workup and precise diagnosis and prognosis of patients with different malignancies. We are presenting the overview of classical and molecular cytogenetic methods, frequency of numerical and structural chromosomal changes in population and the most frequent and specific acquired aberrations of malignant tumors.

        Key words: human and medical cytogenetics, chromosomes, fluorescence in situ hybridization, comparative genomic hybridization.