The occasion of 21CYP mutation in girls with premature adrenarche Premature adrenarche is a heterogeneous condition on its pathogenesis. Scientific discussions in the literature about the frequency occacion of late forms of 21 hydroxylase deficiency among patients with premature adrenarche. The aim of the research: To determine the incidence of 21 hydroxylase deficiency among girls with premature adrenarche Materials and methods of the study: 33 girls with clinical manifestations of premature adrenarche were examined. The age of the examined girls ranged from 5 to 9 years, averaging 6.75 years. Conclusion: According to the molecular genetic studies of CYP 21, a mutation in the given gene was detected in 15.2% girls. 60% Of these have a mutation in the 7th gene of the C1994T and 40% have a mutation of the 4 gene T999A and a heterozygous mutation 2; 4 of the A / G655G gene; T999A. The mutation of the 21 CYP gene correlates with high testosterone, 17OH and androstenedinone values, which indicates violations of adrenal function.