Objectives: To evaluate conservative management of fetal and neonatal ovarian cysts. Methods: We followed the progress of 11 fetal and 2 neonatal ovarian cysts. Results: Ten fetal cysts were simple at recognition, but 8 silently became complex by birth, with ovarian loss in 6/11 cases (54%). In 2 cases where large simple cysts presented for the first time at birth, serious complications occurred, resulting in the death of 1 newborn. Conclusions: If a fetal ovarian cyst is already complex before birth it can be managed conservatively, albeit with loss of the ipsilateral ovary in the majority of cases. As simple fetal ovarian cysts frequently become complex before birth, intervention may be justifiable to preserve the ovary. But any intervention also has the potential for complications, and may be ineffective. Intervention also requires accurate differentiation of ovarian cysts from other abdominal cysts.