In the absence of circulating smallpox, pregnant women should not be exposed to live vaccinia virus contained in the smallpox vaccine. The smallpox vaccine should not be administered to women who are pregnant or might become pregnant within 4 weeks after vaccination because of the risk for fetal vaccinia, a rare but serious infection of the fetus. In addition, persons who have close contact (e.g., household contact or sexual contact) with pregnant women are advised to forego vaccination. To prevent inadvertent exposure of pregnant women to vaccinia virus, screening for pregnancy is a component of pre-event smallpox vaccination programs. To monitor outcomes of pregnancy in women exposed to smallpox vaccines, CDC, in collaboration with the Department of Defense (DoD) and the Food and Drug Administration (FDA), has established the National Smallpox Vaccine in Pregnancy Registry. This report summarizes data from the registry about these exposures. CDC and the Advisory Committee on Immunization Practices (ACIP) recommendations to screen for pregnancy as a contraindication to smallpox vaccination appear to be effective at preventing inadvertent exposures.