Five percent 5-fluorouracil (5-FU), an antineoplastic agent, is often applied to the lower genital tract in the treatment of vaginal and vulvar human papillomavirus infections. Little is known regarding possible teratogenic effects from its topical use in pregnancy. Five cases of antenatal lower genital tract 5-FU use were correlated with pregnancy outcome. Topical 5-FU was applied up to 16 weeks' gestation. Intravaginal doses ranged from 1 to 2.5 g; one patient applied 5-FU to the vulva. Antenatal ultrasound performed on four patients did not show any fetal structural abnormalities. One patient underwent antenatal genetic amniocentesis that detected a 47,XXX complement of chromosomes. All the pregnancies continued without complications and with subsequent term delivery of healthy infants. The unwitting vaginal and vulvar use of 5-FU in pregnancy did not result in significant morbidity or mortality; expectant management of such pregnancies should be considered.