People are exposed to most metal and metalloid elements of the Periodic Table at some stage in their lifetime. At least 15 elements are known nutrients with a defined role in growth, physiology and tissue repair. Good health in the human body requires a balanced level of nutrient elements and the efficiency of inherent protective factors in mitigating the carcinogenic influence of xenobiotic elements and excesses in some nutrient ions. Xenobiotic elements may occur in the body through ingestion in the diet or through occupational or environmental exposures. All are toxic to some extent and at least 12 are carcinogenic under certain circumstances. Identification and classification of putative carcinogens and molecular mechanisms of action depend upon scientific judgement and validation of clinical, epidemiological and laboratory tests. Controversies still exist in the classification of elements such as iron (iron dextran). In epidemiological study, smoking, dietary sufficiency and lifestyle characteristics can have a major impact on the identification of carcinogens. Current emphasis in metal-induced carcinogenesis focuses increasingly on genetic and molecular mechanisms, gene–carcinogen interaction, sensitivities of stem cell populations and epigenetic pathways.