Cytogenetic investigation has been carried out in 4032 newborn infants, 31 of which are found to have karyotype anomalies, which makes 7.7 per 1000 births. The frequency of anomalies in the system of sex chromosomes is 3.2 per 1000. This index is 4.9 per 1000 males, and 1.5 per 1000 females. The frequency of the main types of anomalies turned out to be: XXY--3.0 per 1000 males, XYY--1.0 per 1000 males, XXX--1.0 per 1000 females. The frequency of trisomies of autosomes is 2.0 per 1000 births, trisomy 21 being the main type among them (1.7 per 1000 births). The frequency of structural rearrangements of autosomes is 2.5 per 1000 births, Robertsonian translocations being 1.2 per 1000, reciprocal translocations--1.0 per 1000, and others--0.2 per 1000. The ratio of familial and sporadic mutants was found to be 50%: 50%. Sixty per cent of structural rearrangements are balanced ones, and their carriers does not show any noticeable phenotypic distortions.