Iron deficiency has far reaching consequences on systemic functions apart from the well known feature of anemia. Because iron deficiency anemia is easy to recognize and treat, the non-hematological manifestations of this trace element deficiency have been overlooked. There is a large body of evidence accumulated from animal and human studies to indicate that iron deficiency states are associated with alterations in cellular function, growth, motor development, behaviour and cognitive function. There are consequences for the host's level of immunocompetence against infection, for physical work and metabolic stress, for altered fetal outcome and premature labour in pregnant women. The gastrointestinal functions and other organ systems are also affected as a result of iron deficiency. The purpose of this review is to emphasize the importance of the non-hematological manifestations of iron deficiency and to highlight areas of interest, both to basic scientists and health care professionals.