The authors review literary data and own investigations indicating that anomalies of follicular ripening and ovulation carry a substantial risk of ensuing reproductive abnormalities. Absence of ovulation is conducive to sterility, while delay of the follicular maturation process predispose to the development of an overripe ovum. The degenerative changes that characterize overripeness are conducive to the occurrence of chromosome and anatomic anomalies in the fertilized ovum. The same process predisposes to early abortion and, presumably, to monozygous twinning. Delayed ovulation is predictably associated with corpus luteum inadequacy. Clinically, this phenomenon is frequently associated with postconception bleeding, occult abortion, extrauterine pregnancy and implantation on the lower uterine segment (placenta praevia). Multiple ovulation predisposes to heterozygous twinning.