More than 85% of prenatal ovarian cysts have a follicular or luteal origin. Their natural history is a spontaneous involution. However, adnexal torsion resulting in the loss of the ovary can occur at any time of the evolution. Pre and postnatal changes in the sonographic aspects allow to choose the appropriate therapeutical indications: conservative approach, laparoscopic surgery, or percutaneous aspiration. Prenatal aspiration must be avoided. The last prenatal sonographic examination should be performed as close as possible from the end of the gestation, and the first postnatal echography within the first 24 hours of life. Surgery of prenatal complicated cysts has to be planned a few days after birth. Uncomplicated prenatal cysts will be treated depending on size and echographic patterns at birth.