The obstetric outcome (abortions, stillbirths, prematurity, mature births, and congenital abnormalities) in a group of 1522 consecutive pregnant patients who had smallpox vaccinations during recent pregnancies was compared to that in a similar control group of 2024 consecutive pregnant patients who did not receive any antenatal vaccination. Results showed that smallpox vaccination during pregnancy did not increase the rate of stillbirths, premature births, or congenital abnormalities in patients who had been vaccinated at least once before. However, it was noted that women vaccinated during the first trimester of pregnancy more often had children with clubfoot. Therefore, unless there is an immediate risk, we recommend delaying smallpox vaccination during pregnancy until the second or third trimester. However, during an epidemic, vaccination should be done regardless of gestational age.