Haemophilia is a serious hereditary bleeding disorder that results in the inability of the blood to clot properly, leading in severe cases to uncontrolled bleeding, either spontaneous or related to minor trauma. Although a person with hemophilia does not bleed more or faster than a person without hemophilia, they bleed for longer periods of time and recurrent bleeding can lead to significant deterioration, especially in the joints.

In late 1984, it was discovered that heating extracts from plasma could inactivate viruses; the hepatitis B virus, which proved resistant to treatment, was then eliminated, and it was by chance that HIV was discovered to be inactivated. However, France's treatment capacity is insufficient, and it refuses to import blood from abroad (particularly from the United States), mainly for four reasons:

- for ethical reasons: the blood used by American laboratories comes from trade exploiting poor countries ;
- for quality reasons: overheating would have caused a decrease in the activity of the product, and amplified the risk of anticoagulant antibodies circulating in the recipient;
- for financial reasons: the import of heated foreign products produced by foreign German and American firms (Behring, Travenol, Alpha, Armour, Cutter and Kabi) represented a certain cost;
- for strategic reasons: the importation of foreign heated products, available from March 1983, called into question the monopoly of the National Centre for Blood Transfusion on the French market for blood products. However, in 1983, the CNTS had not mastered the production technique for heated products. The production unit will be operational from 1984, but was not planned from the outset to eliminate the HIV virus.

Until 1985, unheated products were distributed only to haemophiliacs, while heated products were reserved for HIV-negative patients or those who had never been transfused, due to the scarcity of products at the time. Because of this, stocks of unheated products, worth 34 million francs, were left in circulation and reimbursed until 1 October 1985.

Public opinion was not really alerted until mid-1985, when the Prime Minister announced the compulsory screening of blood donors from 1 August (decree of 23 July 1985). At that time, 95% of haemophiliacs were already contaminated.

The extent of the tragedy was only known in August 1986, with the publication of a report by the CNTS, which stated that one haemophiliac 1/2 had been contaminated, about 2,000 people.

It was not until five years later, at the end of April 1991, thanks to the investigations of the journalist Anne-Marie Casteret, that the truth finally came out in the press: batches of contaminated blood (some with the AIDS virus) were knowingly distributed to haemophiliac patients during transfusions in the same year 1985. The result of the accounts: half of the haemophiliac population, i.e. several thousand people, were infected with diseases and several hundred people were infected with the AIDS virus.