Congenital adrenal hyperplasia (CAH) is a group of seven autosomal recessively inherited disorders of various enzymes participating in adrenal steroid hormone synthesis. Patients present with various symptoms depending on the nature and severity of the enzymatic block. More than 95% of all CAH patients suffer from 21-hydroxylase deficiency. The genetic background is well characterized for all CAH subtypes. Characterization of their genetic background has provided important pathophysiologic understanding of steroid biosynthesis disorders. Genotyping is important for confirming diagnosis, determining prognostic factors, and for genetic counseling for family planning and may reveal new therapeutic approaches.