Congenital adrenocortical hyperplasia is a complex endocrine disorder of importance to the paediatric urologist because it produces an intersex state in the female and precocious virilisation in the male. The excessive secretion of androgens by the foetal adrenal cortex commences in early foetal life at some time after the differentiation of the internal genitalia from the Wolffian and Mullerian duct systems, but before complete differentiation of the external genitalia. Varying degrees of virilisation are present in the female at birth; the male does not at this stage exhibit any striking abnormality, though in both sexes there will be progressive virilisation of the untreated case.