CYP21A2 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: This study identifies the spectrum and frequencies of CYP21A2 variants as well as genotype-phenotype correlations in a group of 48 adult patients with CCAH due to 21-hydroxylase deficiency treated in the Department of Endocrinology at the University Hospital in Krakow, Poland.