Menarche is a sign of puberty and the beginning of ovarian and other endocrine functions relating to reproduction. It is an important event demonstrating the end of childhood and the start of reproductive years for each woman that is preceded by the complex process of some hormonal changes in the puberty period. Moreover, it is an important clinical indicator of girls’ physical, nutritional, and reproductive health. Early age at menarche, as the onset of menstrual periods in girls, has a substantial effect on their physical and sexual health and is related to the increased risks of unfavorable health outcomes. Further, menarche appears to be associated with several risk factors of emergent chronic disease. In recent decades, the age at menarche has shown a gradual decline from 16-17 years to less than 13 years. Evidence indicates that childhood obesity is related to earlier menarche. Finally, this change may be partially explained by the global epidemic of obesity.