As a result of refinements in Prenatal Ultrasonography (US), neonatal ovarian cysts are more frequently encountered than in the past. Between January 1981 and December 1990, 21 consecutive fetuses with ovarian cysts were followed up by ultrasonography. 23 ovarian cysts were diagnosed between 28 and 38 weeks gestation. 18 cysts were initially large cysts (more than 50 mm in diameter). In 9 cases, an anechoic cyst was observed and a US-guided needle aspiration of the cyst was performed (2 antenatally and 7 postnatally). Ultrasonographic patterns of complicated cyst were observed in 3 fetuses. After a postnatal ultrasound control, 11 infants were operated on: 8 surgical interventions were required for complicated cysts (torsion: 4, hemorrhage: 4), 3 cases irrespective of their sonographic appearance in our initial experience. In the remaining cases, spontaneous resolution was followed by repeated ultrasonographic examination. Prenatal ultrasonography today allows diagnosis of ovarian cysts and may suggest antenatal complications. To preserve as much ovarian tissue as possible, cysts greater than 50 mm in diameter should be candidates for percutaneous aspiration and complex cystic masses should be operated on.