Sexual maturity before the age of eight in girls and ten in boys. Both show an early development of secondary sexual characteristics. Girls’ breasts increase in size, and menstruation is usually early. In boys the penis, testicles, pubic hair and underarm hair grow, the beard begins to grow, and somewhat later the larynx increases in size and the voice breaks. As a growth spurt is usually associated with puberty, such children are often tall for their age, but this in itself need not cause anxiety because an early growth spurt is often shorter than usual. The cause of early puberty is not always known; this is the case in 40 per cent of boys and 85 per cent of girls. The cause can be a pituitary tumour, which causes overproduction of sex hormones (FSH and LH); this can also occur because of hyperactivity of the sex cells themselves (in the testicles, ovaries or adrenal cortex). If the adrenal cortex is overproducing at birth, in a girl this can give rise to male external genitals, while the internal genital organs are female (pseudohermaphroditism). The abnormality is caused by excess male sex hormones, which can make it difficult to establish the child’s sex at birth. Diagnosis is by family history, physical appearance and extensive laboratory tests. Treatment is aimed at reducing the abnormal sex hormone content, by surgery, radiation therapy or medication. Children often have difficulty if they reach sexual maturity early because they look older than they are. Early sex education and good psychological treatment are important.