Smallpox is a highly infectious disease, which, in 1980, was declared eradicated by the World Health Organization as a result of successful vaccination campaigns. Because of its highly infectious nature and historical 30% mortality rate, the disease has possibly been developed as a biological weapon. Variola, the virus that causes smallpox, is readily transmissible from person to person during the incubation period, before infected individuals show signs of illness. When a victim develops the characteristic rash and viral syndrome associated with smallpox infection, the disease requires complex isolation and possibly quarantine. Diagnosis can be confirmed in a high-containment laboratory. The only effective treatment for smallpox is rapid administration of smallpox vaccine. © 2005 Elsevier Inc. All rights reserved.