The rubella virus is a potent human teratogen. The highest risk of this infection occurs during pregnancy, as the virus may cause fetal damage known as congenital rubella syndrome (CRS). Since the rubella vaccine is made with attenuated live virus, there is a high level of anxiety concerning exposure during pregnancy. Although no case of CRS has been proved in children of immunized susceptible pregnant women, a risk below 1.6% cannot be ruled out. Our main purpose was to evaluate the occurrence of CRS in women who were vaccinated against rubella and did not know that they were pregnant, or became pregnant within 30 days after vaccination. We collected, prospectively, data on 171 pregnant women who were susceptible at the time of vaccination and compared them with data on the total population of pregnant women in the state of Rio Grande do Sul (RS), Brazil. A serologic sample was collected in 149 infants of susceptible mothers. A total of 10 infants (6.7%) had anti-rubella antibodies. When these were compared with the results obtained in the total population of births in RS, no difference was found in mean birth weight, low birth weight and sex. None of the ten infants with IgM(+) presented congenital defects involving CRS, during the physical examinations performed at the time of birth and at 3 months of age. Our study allows the safety of rubella vaccination to be extended to pregnant women.