Mercury is a silvery-white chemically active transition metal without known physiological role. It is also a toxin accumulated in living organisms--especially in the aquatic creatures (fish and shellfish). Mercury compounds are involved in biogeochemical cycles (especially atmospheric and hydrobiologic), and thus they become contaminants of food. Such process is facilitated by the increasing environmental chemization. Toxic effects of mercury compounds result from their high affinity to sulfur (sulfhydryl groups of amino acids), accumulation in parenchymal organs, metallic mercury lipophilicity as well as long biological half-life period. In Poland the major sources of mercury exposure in diet are fish products and mushrooms. The role of mercury in human toxicology was presented in the work, along with a review of the literature concerning mercury content in selected food products in Poland. In general, most of foods do not pose a threat to consumers' health. Some restrictions in the amount of predatory fish and mushrooms consumed by pregnant and breastfeeding women as well as small children should be however recommended.