TRUE RISKS AND THEORETICAL RISKS: The texts ruling the obligation of the physician to inform the patient appears not to include theoretical risks in their application. In France however, the field of blood transfusions extends this obligation to the theoretical risk of potential transmission through the blood of the infectious agent responsible for Creutzfeldt-Jakob's disease. UNANSWERED QUESTIONS: From an ethical point of view, is information on the theoretical risk of transmission founded? From a formal point of view, the means used for such an extension (i.e.,a bulletin) is debatable; was this an adequate measure? THE RETURN OF COMMON SENSE: If we look at the earlier texts, the principle of an obligation to inform the patient of the theoretical risks does not appear widespread or even confirmed. Do these text simply the return of "common sense"? And if so, to what extent does it encourage the illusion of a zero risk...?