Menarche is a rather late event in puberty and usually occurs 6 months after PHV is achieved. The age that menarche occurs varies and is dependent on the interaction between genetic and environmental factors. US study performed using data from the Third National Health and Nutrition Examination Survey, demonstrated that the mean age at onset of menarche was 12.1 years for black girls; 12.2 for Mexican American girls; and 12.7 for white girls. Age at menarche in Asian is similar to Mediterranean girls; mean menarcheal age in Hong Kong and Japan is 12.38 and 12.2 years, respectively, and in Greece or Spain 12.27 and 12.34, respectively.