Ovarian cysts can be demonstrated in the ovaries of fetuses and full term infants at birth. Small cysts involute spontaneously during fetal life or within the first few months of life. Large cysts may cause mechanical complications or respiratory distress. Sonographic detection of fetal ovarian cysts has been reported, as well as intrauterine surgical treatment. The sonographic findings and the outcome of the smaller and the complicated cysts were studied in 25 pregnant women. Uncomplicated fetal ovarian cysts should be monitored by weekly examination until delivery. Huge ovarian cysts may be an indication for cesarean section; or, intrauterine aspiration may be the alternative. Complicated fetal ovarian cysts represent an indication for neonatal surgery.