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The menarche stands as our primary indicator of the onset of sexual maturity in females. The age at which this milestone occurs has therefore become one of the major parameters of maturation rates among individuals, or among groups, and the wide range of variation in age at menarche makes it a useful parameter. The factors which operate to create variability in menarcheal age are many, and involve hereditary and environmental determinants. Their interactions are quite complex and any attempt to isolate significant associations must adopt a multifactorial design. Only in this way will the nature of the determining factors, particularly those associated with the external environment, be discovered.