Congenital adrenal hyperplasia (CAH) refers to a family of inherited disorders of adrenal steroidogenesis in which each disorder is characterized by a specific enzyme deficiency that impairs cortisol production by the adrenal cortex. The enzymes most commonly affected are 21-hydroxylase (21-OH), 11beta-hydroxylase, 3beta-hydroxysteroid dehydrogenase, and less often, 17alpha-hydroxylase/17,20-lyase and cholesterol desmolase. Many of the corresponding genes for the described enzymes have been isolated and characterized, and specific mutations causing CAH have been identified. In classical CAH (simple virilizing and salt wasting forms), androgen excess causes external genital ambiguity in newborn females and progressive postnatal virilization in both sexes. In nonclassical CAH, 21-OHD is partial and occurs with milder symptoms. A deficiency of 11beta-Hydroxylase deficiency results in ambiguous genitalia in the newborn genetic female and androgen excess and hypertension in both males and females. In 3beta-hydroxysteroid deficiency adrenal and gonadal androgen production is deficient resulting in incomplete genital development in genetic males and limited androgen affect in females. Two less frequent causes of CAH 17alpha-Hydroxylase/17,20-lyase and cholesterol desmolase result in external female genitalia in both sexes. Hormonal diagnosis is described for each disorder.