Deficiency of 21-hydroxylase constitutes the most frequent form of Congenital adrenal hyperplasia (CAH) and is classified into classical and nonclassical (NC) forms. The type of the molecular defect determines the severity of the phenotype with a high degree of concordance for the classical genotypes but with lower concordance for the NC genotypes. The clinical expression of NC-CAH is quite variable ranging from an asymptomatic state to premature pubarche, hirsutism, acne, menstrual irregularities, infertility and increased rate of spontaneous abortions. Basal and/or ACTH stimulated 17-hydroxyprogesterone (17OHP) values,>> 5 ng/ml and >10 ng/ml, respectively are currently applied to diagnose NC-CAH. Glucocorticoid administration to patients with NC-CAH is determined by the clinical manifestations. During pregnancy, steroid replacement therapy and adequate monitoring reduce the risk of spontaneous abortions. CYP21A2 genotyping of the partner of a prospective mother with NC-CAH is controversial. Most likely it should be performed if the mother carries a classical mutation.