The study of prevalence of Cx26 gene mutations in children suffering from congenital and prespeech non-syndromal hypoacusis was conducted in Russian population since 2001. The screening of this group of children showed that 35delG mutation occurred in 53%. This index depends on the region and clinical characteristics of the groups studied. Thus, in the family burden it increased to 65% and more. The article presents clinical characteristics of hearing problems caused by 35delG mutation in Cx26 gene. Clinical evidence was obtained on 197 patients with the affected genotype (146 homozygotes and 51 heterozygotes by deletion). Most of deletion homozygotes were diagnosed early (under 1 year) and had bilateral neurosensory hypoacusis with frequent severe hearing loss (75.7%). No family burden was seen in 47% patients with abnormal genotype. In the group studied only 24% cases had no familial burden. 20% children were born by mother with abnormal pregnancy and delivery, 2.5% had the history of severe infections except meningitis, 11.7% - of first year diseases. Cx26 gene mutations were diagnosed in half cases of hypoacusis in children whose parents attribute hearing loss to administration of antibiotics.