In the context of its plan to fight against bioterrorism, the Ministry of Health asked the Institut de Veille Sanitaire to evaluate the epidemic risk from a release of the small pox virus, and to make recommendations on potential vaccination strategies to be implemented. A benefit/risk assessment of various vaccination scenarios, including vaccination of the whole French population, was carried out to evaluate the severity of a terrorist action threat. This analysis concludes that at this stage, vaccination action does not seem to be justified. Even in the case of a real threat, the vaccination of frontline healthcare personnel, and in particular of contacts of cases, must be given priority.