The effect of clomiphene citrate (CC) on the incidence of congenital malformations in newborn infants was assessed from the outcome of 1034 pregnancies after CC-induced ovulation recorded at nine university hospitals in a 5-year period. Of these pregnancies, 14.2% ended in abortion, 0.5% in ectopic pregnancy, 0.1% in molar pregnancy, and 1.6% in stillbirth. In all, 935 infants were born, and 21 (2.3%) showed visible malformations. This incidence of malformations was not significantly different from that in 30,033 infants (1.7%) after spontaneous ovulation (spontaneous ovulation group), and the types of malformations after CC treatment were similar to e those in the spontaneous ovulation group. These data indicate that CC has no teratogenic effect.