The concept of risk cannot be limited to simply knowing the probability of occurrence and the seriousness of the damages caused. It's a matter of social construction and numerous elements contribute towards its perception and acceptability. These elements have been studied for 20 years or so. Some of these elements influence risk perception such as awfulness, unfamiliarity, the number of people exposed to it, other elements influence its acceptance such as individual perceptions, social factors, ethics and equity. Their knowledge allows a better understanding of the evolution of perception and of the risk acceptability in general and transfusion risk in particular.