Adolescence is characterized by a large growth spurt and the acquisition of adult phenotypes and biologic rhythms. During this period, iron requirements increase dramatically in both boys and girls as a result of the expansion of the total blood volume, the increase in lean body mass and the onset of menses in young females. The overall iron requirements increase from a preadolescent level of approximately 0.7-0.9 mg Fe/d to as much as 2.2 mg Fe/d or perhaps more in heavily menstruating young women. These increased requirements are associated with the timing and size of the growth spurt as well as sexual maturation and the onset of menses. The available data on iron intakes in adolescents suggest that adolescent girls are unlikely to acquire substantial iron stores during this time period because intakes may average as little as 10-11 mg Fe/d. The bioavailability from diets in developing and industrialized countries indicates a negative iron balance is likely in many female populations. The low iron stores in these young women of reproductive age will make them susceptible to iron deficiency anemia during pregnancy because dietary intakes alone are insufficient, in most cases, to meet the requirements of pregnancy.