There is great concern that smallpox could be used for bioterrorism. The disease has a high mortality rate and can be spread by aerosols, and immunity in the population is low. Although an initial release of smallpox could infect a large number of people, secondary spread would likely be slow because of the long incubation period and the close contact required for transmission. Hospital personnel and household contacts are at the greatest risk of becoming infected. An outbreak of smallpox will be controlled through surveillance, containment, vaccination, and isolation of cases-the strategy used to eradicate the disease globally in 1978. Pre-exposure vaccination is recommended for hospital personnel likely to be exposed to smallpox while caring for patients during an outbreak.