Bovine spongiform encephalopathy (BSE), or "mad cow disease", as well as Creutzfeldt-Jakob-Disease in humans, have recently been attracting public attention. The European Society of Gastrointestinal Endoscopy (ESGE) has issued guidelines on the topic (Endoscopy 1997; 29: 203-4), which were accompanied by a review article by T. Ponchon ("Transmission of hepatitis C and prion diseases through digestive endoscopy: evaluation of risk and recommended practices", Endoscopy 1997; 29: 199-202) dealing with the potential transmission of BSE and hepatitis C through gastrointestinal endoscopy. The following article on prion diseases in general provides a more in-depth overview of these disorders and their epidemiology and pathophysiology.