EPIDEMIOLOGY ADN PHYSIOPATHOLOGY: Hereditary haemochromatosis is the most common genetic disease in France. Its frequency is on average 1 out of 300 French individuals. It is due to excessive dietary iron absorption, leading to accumulation of iron in the body. Mutations of the HFE1 gene are responsible for the majority of the case of haemochromatosis. FROM A CLINICAL POINT OF VIEW: The first clinical manifestations (weakness, sexual dysfunction, arthralgia, cardiac symptoms, dyspnoea on effort) can occur after the age of 30 years in men and 35 years in women (protected for longer by menstruation, pregnancy and delivery). In the absence of diagnosis, severe complications can develop during the 5th decade: nervous breakdown, arthropathy, heart failure, diabetes mellitus, cirrhosis with risk of progression towards carcinoma, responsible for handicaps and premature death. DIAGNOSTIC ELEMENTS: The diagnosis is evoked in the case of an increase in transferrine saturation (>45%), associated or not with excessive ferritin plasma levels. It is confirmed by the genetic test, showing homozygotes for the C282Y mutation or compound heterozygotes for the C282Y and H63D mutations on the HFE1 gene. RMI quantifies hepatic iron loading and generally avoids the need for a liver biopsy. The differential diagnosis must exclude secondary iron overload due to chronic transfusions in congenital or acquired blood diseases, a polymetabolic syndrome, chronic viral or alcoholic hepatic diseases and porphyria cutanea tarda. EFFICIENT TREATMENT: Today, haemochromatosis is still treated by phlebotomy. This consists in withdrawing 400 to 500ml of blood every week at the initial depletion stage and subsequently a maintenance therapy in order to maintain ferritin levels below 50 ng/ml. Paradoxically and through ignorance, hereditary haemochromatosis remains a serious disease, although its diagnosis is easy and the treatment simple and effective.