The risk to a fetus after rubella vaccination of its mother is unknown. The Center for Disease Control has compiled information from the pregnancies of 343 women inadvertently given rubella vaccine shortly before or after conception. The pregnancies of 145 women were terminated by therapeutic abortion, and rubella vaccine virus was recovered from the products of conception of nine women, including six of the 28 known to be seronegative to rubella at the time of vaccination. None of the 172 infants carried to term had either clinical or serologic evidence of rubella infection, including 38 infants of women known to be susceptible and 12 additional women estimated to be susceptible at the time of rubella vaccination. On the basis of the binomial distribution, the maximum risk of fetal infection after maternal rubella vaccination is between 5 and 10 per cent. The actual risk is probably less.