In a multicenter trial we retrospectively evaluated the clinical and sonographic data of 49 neonatal ovarian cysts, 44 of which were detected prenatally and 5 on the first day after delivery. Of the 44 prenatally detected cysts 39 were purely cystic, 5 echogenic or had a mixed pattern. In 20 patients the cystic appearance changed during delivery from purely cystic to a mixed pattern being independent on the size of the cyst. 26 of the 44 cysts were treated surgically. Salpingotorsion was found in 8 and was independent on the size of the cyst. In 15 a salpingo-oophorectomy or oophorectomy was performed, in 11 the ovary was saved. 23 patients were followed sonographically: 15 cysts showed complete resolution within 14 months without correlation to the sonographic pattern. The volume of these cysts varied between 5 and 71 ml. Neonatal ovarian cysts disappear spontaneously frequently and rarely cause severe symptoms. The authors recommend follow-up by ultrasound as the primary modality. Surgical intervention is recommended only if the cyst is space-occupying and percutaneous puncture can not be performed or in the case of emergency.