Twenty-seven neonatal ovarian cysts were diagnosed in utero during a 13-year period; 9 were complicated and 18 were initially simple, but 8/18 showed evidence of complications in utero or soon after birth, leaving only 10 simple cysts. One simple and 4 complicated cysts were surgically excised early in the study period; 2 simple cysts were treated by needle aspiration at birth because of their large size. The remaining 20 cases were initially managed conservatively. All simple cysts and 10/13 complicated cysts regressed completely within 12 months; 3 that failed to regress were surgically excised. Nineteen patients who did not undergo a laparotomy had ultrasonographic (US) examinations from 3 months to 9 years after birth. Echography showed both ovaries in all 9 girls who had simple cysts at birth and in 2 of the 10 with complications. In the other 8 complicated cases only one ovary was detected at follow-up. Pre- or post-natal aspiration of simple cysts 4 cm or more in diameter is recommended, while conservative management seems appropriate in the absence of symptoms for simple cysts of less than 4 cm and complicated cysts of any size tending to involute after birth.