The age of menarche is determined by a combination of factors which include genetic influences, socio-economic conditions, general health and wellbeing, nutritional status, certain types of exercise, and family size. It is well known that delayed menarche is a feature of chronic disease. The role of birth weight and proportion of body fat in menarcheal age has received considerable attention. Girls who consume more (energy-adjusted) animal protein and less vegetable protein at ages 3 to 5 years have an earlier menarche. Conversely, a diet high in fibre is associated with a delayed menarche. Family size and birth order also influence age of menarche. The significance of early-life exposure to environmental or hormonally active chemicals is also a growing area of debate. Referral is essential earlier if secondary sex characteristics have not developed or there appear to be anatomical disorders of the genital tract or signs of a chromosome abnormality.