Smallpox vaccination of civilian volunteer health-care workers began on January 24, 2003. As of February 4, a total of 37 states and counties have received shipments of smallpox vaccine, and 18 states and counties have begun smallpox vaccination; no serious adverse events have been reported. To monitor the occurrence of adverse events associated with vaccination, both those expected on the basis of previous experience and possible new unexpected adverse events, CDC and state health departments have established the Smallpox Vaccine Adverse Events Monitoring and Response System. The system also will be used to monitor the effectiveness of contraindication screening, identify new contraindications, and coordinate the distribution of vaccinia immune globulin (VIG) and cidofovir to the civilian population. This notice describes the components of the system, delineates roles and responsibilities, and explains how data from the system will be compiled and communicated.