Geophagia, the eating of dirt, usually clay, has been recorded in every region of the world both as idiosyncratic behavior of isolated individuals and as culturally prescribed behavior of particular societies. The behavior has long been viewed as pathological by the medical profession, and it has been claimed to be both a cause and a consequence of anemia. While there is now reason to believe that the consumption of some clays may interfere with the absorption of elemental iron, zinc, and potassium, there is little evidence for the position that geophagia, especially its culturally prescribed form, is caused by anemia. These and other maladaptive consequences of clay consumption may be offset by the adaptive value of its antidiarrheal, detoxification, and mineral supplementation potentials.