46,XX DSD

46,XX DSD comprises the most common group of genital variations, with congenital adrenal hyperplasia (CAH) being the most important, not only because of its frequency but also because of its life-threatening complications without treatment. The different conditions are described, showing the range of genetic and enzymatic anomalies that lead to excess androgen production, causing abnormal virilisation of a female foetus. The non-hormonal anatomical defects of genital development are also mentioned.