The risk of bearing a child with chromosomal defects increases once the mother reaches the age of 35; the principal indication for chromosomal examination of the fetus is that the pregnant woman is "older". Chromosomal examination of new-born babies is indicated if it is suspected that dysmorphic features may depend on cytogenetic deviation. Other indications include suspicion of so-called fragile X syndrome or rare congenital disorders such as Fanconi's anemia, Xeroderma pigmentosum etc. Chromosomal examination is routine today in investigation of suspected or verified hematological diseases. Nevertheless the possibilities of cytogenetic techniques have not yet been used to the full in diagnostics, assessment of prognoses, choice of therapy and follow-up of disease.