This article briefly describes how iron lies at the center of a host-pathogen battle for nutrients and why there are many theoretical reasons to suspect that administration of supplemental iron might predispose to infection. This is supported by in vitro and small animal studies, but meta-analysis of human epidemiological and intervention studies has found little evidence for most disease outcomes. Supplemental iron does appear to increase susceptibility to malaria as measured by a variety of malariometric indices. However, even in malarious areas, iron appears beneficial in iron-deficient subjects. The concerns about iron supplementation programs for children seem to be confined to Sub-Saharan Africa and to areas of high malaria endemicity, where it will be necessary to adopt a cautious approach to supplementation based either on screening out iron-replete children or combining iron administration with effective disease-control strategies.