The congenital adrenal hyperplasias (CAH) are a group of inherited enzymatic defects of adrenal steroid biosynthesis. Deficiencies of each enzyme required in the steroid biosynthesis pathway are known, and these deficiencies are all inherited as autosomal recessive disorders. During pregnancy, maternal and fetal problems are confined to women who have 21-hydroxylase deficiency (P450c21 deficiency), 11-hydroxylase deficiency (P450c11 deficiency), and 3 beta-hydroxysteroid dehydrogenase deficiency (3 beta HSD deficiency), because other adrenal enzyme deficiencies are not compatible with fertility. The interposition of the placenta on the hypothalamic-pituitary-adrenal axis and other endocrine changes during pregnancy impact considerably on the clinical evaluation of the congenital adrenal hyperplasias. Successful management of CAH in pregnancy requires a firm knowledge of normal adrenal anatomic and endocrine changes that occur during gestation. Women with severe forms of CAH have decreased fertility rates because of oligo-ovulation, and successful conception requires a combination of good therapeutic compliance, careful endocrine monitoring, and often ovulation induction. From a fetal and neonatal standpoint, accurate prenatal diagnosis of 21-hydroxylase deficiency and 11-hydroxylase deficiency is now possible, which allows for prenatal treatment in an attempt to minimize clinical problems in the neonates. Prevention of masculinization of affected female fetuses by corticosteroid suppression has been attempted in both 21-hydroxylase deficiency and 11beta-hydroxylase deficiency CAH, with variable degrees of success. This review provides an overview of the congenital adrenal hyperplasias and their management during pregnancy.