Generally, live-virus vaccines are contraindicated for pregnant women because of the theoretical risk of transmission of the vaccine virus to the fetus. Advisory groups recommend avoiding pregnancy in the immediate period after administration of such contraindicated vaccines (CVs) and stress benefit-to-risk evaluation for live or inactivated vaccines regarding pregnancy. Given the limited available data and theoretical risks associated particularly with live-virus vaccines, inadvertent immunization with CVs may lead to elective termination of pregnancy (ETP), despite advisory group statements that "vaccination is not ordinarily an indication to terminate the pregnancy." The Vaccine Adverse Event Reporting System (VAERS), a national passive surveillance system managed by the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC), accepts reports of adverse events after vaccination. The objectives of this review were to describe reports of ETP in VAERS and characterize the circumstances of inadvertent administration of vaccines to pregnant women among ETP reports. We reviewed VAERS reports of ETP submitted from 1990 to 2006. Reports of ETP for reasons other than vaccination during or shortly before pregnancy, such as fetal abnormalities or deaths, were excluded. Of 80 ETP reports, 62 (78%) originated from the US; 79 (99%) were reported by manufacturers. Median age of vaccinees was 26 years (range: 13-43 years; 67 reports). Seventy-three vaccinees (91%) received a single vaccine; 65 (81%) received at least one live-virus vaccine. In 48 (60%) ETP reports, vaccinees were unaware of pregnancy at time of immunization. In 15 (19%) reports, vaccinees became pregnant within 3 months of vaccination; in 13 (16%) reports, vaccinees might have been pregnant before vaccination; in 4 (5%) reports, information was missing. All 80 reports of ETP involved vaccines for which possible effects on fetal development are unknown. However, no cases of vaccine-associated congenital rubella or varicella syndromes have been reported in the medical literature. Also, these syndromes have not been reported to varicella or rubella vaccine pregnancy registries. VAERS has the limitations of passive surveillance systems. Under-reporting of ETP in VAERS could be substantial. More attention may be needed to assess the likelihood of pregnancy when administering vaccines to women with child-bearing potential, and to inform women who learn they are pregnant shortly after being immunized of current information on risks. Quantifying the frequency of ETP related to CVs and the risk (if any) to the fetus of such vaccines can help to inform policy, practice, and individual decision making. Good quality information may be obtained from controlled observational studies.