Iron has a central role in haem synthesis and the oxygen-carrying capacity of the blood. Iron-related enzymes are involved in cell proliferation, energy production, immunocompetence and a wide range of other key functions. Regulation of iron stores in the human body is not well understood but some iron is excreted in perspiration and through the skin, hair and nails. Excess iron can be toxic, mutagenic and genotoxic and is now known to be a cause of hepatocellular carcinoma in patients with hereditary haemochromatosis or other forms of iron overload. Principal carcinogenic risks associated with iron concern the haematite mining industry where underground workers are exposed to dusts containing haematite, silica, radon and the carcinogenic elements arsenic, lead, cadmium, chromium and nickel. Silicosis and radon exposures are considered to pose the greatest risk. Iron dextran injections, used for many years for treatment of iron deficiency anaemia, have been shown to cause injection site sarcomas in laboratory animals and have been identified as reasonably carcinogenic to humans. This has not been confirmed in clinical studies, and in the 22 years following its introduction only nine cases of human injection site sarcoma have been identified, and tumour type was not consistent. In view of the ability of iron to induce formation of reactive oxygen radicals and oxygen stress and to create a microenvironment favourable to tumour growth, therapeutic and dietary controls are necessary to deprive neoplastic cells of iron in cancer patients.