Genetic haemochromatosis (GH) is the most common, autosomal recessive disorder in Northern Europe. The studies which led to the identification of the HFE gene are described. In the UK over 90% of patients with GH are homozygous for the C282Y mutation of this gene. This mutation is confined to populations of European origin. The significance of another mutation, H63D, in causing iron overload is less certain. Preliminary studies on the localization of the protein and the effects of the mutations are described. Genetic testing and the measurement of iron status now provide the means to allow for widespread testing for the prevention of iron overload and its consequences. However, questions remain about the clinical penetrance of GH.