The trace element zinc is an essential micronutrient for the proper functioning of the immune system. Zinc deficiency leads to impaired function of the unspecific and specific immune response and consequently to an increased susceptibility to bacterial, viral and fungal infections. Immunological defects are not only seen in pronounced but even in marginal and moderate zinc deficiency. Lack of zinc is especially harmful for the development of the immune system, which stresses the importance of a balanced zinc level during pregnancy. However, gestational zinc deficiency due to an imbalance between intake and increased requirements is a common problem world-wide. In animals, gestational zinc deficiency results in reduced thymic and spleen size and depressed active and passive immunity in the infant. For example, depressed immunoglobulin levels, altered antibody repertoire, reduced proliferative response of lymphocytes and diminished neutrophil functions have been reported. Interestingly, immune defects caused by prenatal zinc deficiency, such as depressed antibody levels and lymphocyte proliferation, may even persist in subsequent generations and are not reversible by postnatal zinc administration. Since gestational zinc deficiency is a common problem throughout all cultures and socioeconomic levels, it might have immense consequences for the health status of the population. Based on a summary of the immunobiology of zinc, this article reviews the significance of zinc deficiency during pregnancy and the effect of gestational zinc deficiency on passive and active immunity in the infant. It provides a rational basis for both immunological laboratory investigations and field studies, such as large community-based zinc supplementation trials in pregnant women.