There are two major disturbances of iron balance: iron deficiency and iron overload. Iron-deficiency anemia is a major problem in developing countries and affects between 500 million and 600 million people worldwide. While iron overload is much less prevalent, it has a number of major pathologic sequelae and there have been recent suggestions that even modest increases in the body's iron stores may have pathologic associations. To understand the ways in which iron balance can be disturbed, it is necessary to have an understanding of how losses from the body are matched by the absorption of iron in different dietary settings as well as the limits of this regulatory control.