This Policy Statement was retired January 2006. After an extensive worldwide eradication program, the last nonlaboratory case of smallpox occurred in 1977 in Somalia. In 1972, routine smallpox immunization was discontinued in the United States, and since 1983, vaccine production has been halted. Stockpiled vaccine has been used only for laboratory researchers working on orthopoxviruses. In recent years, there has been concern that smallpox virus stocks may be in the hands of bioterrorists, and this concern has been heightened by the terrorist attack on the World Trade Center and the Pentagon on September 11, 2001. Because most of the population is considered to be nonimmune, there is debate as to whether smallpox immunization should be resumed. This statement reviews the current status of smallpox vaccine, the adverse effects that were associated with smallpox vaccine in the past, and the major proposals for vaccine use. The statement provides the rationale for a policy based on the so-called ring vaccination strategy recommended by the Centers for Disease Control and Prevention, in which cases of smallpox are rapidly identified, infected individuals are isolated, and contacts of the infected individuals as well as their contacts are immunized immediately.