A hypothesis is presented to explain the abnormalities and syndromes seen in congenital adrenocortical hyperplasia and to unify the syndromes of adrenocortical hyperfunction seen in the human adult. It is suggested that phylogenetically only sex hormones were originally elaborated by the adrenal cortex. Subsequently, the adrenal cortex acquired the ability to convert progesterone to corticosterone and aldosterone in order to facilitate renal conservation of sodium. Still later the process of 17 hydroxylation and presumably corticotrophin secretion were evolved. The relation of this hypothesis to adrenocortical hyperfunction is discussed.