The antenatal diagnosis of ovarian cysts poses a therapeutic dilemma because the natural history of these lesions is not well known. A retrospective review from 1980 to 1989 showed 29 ovarian cysts in 27 patients diagnosed by prenatal ultrasonography performed between 28 and 36 weeks of gestation. Nineteen cysts were initially observed. Eleven cysts resolved (diameter less than 2 cm), three are decreasing, three were lost to follow-up, and two underwent resection. Eight patients underwent surgical exploration immediately following birth. The diagnosis of benign ovarian cyst was confirmed histologically in all cases. A review of the literature showed an additional 230 cases of antenatally diagnosed ovarian cysts. Simple cysts of the ovary tend to resolve spontaneously and, therefore, may be treated conservatively. Serial ultrasonography allows accurate diagnosis and long-term assessment of ovarian cysts in the neonate and may prevent unnecessary oophorectomy. Patients with cysts larger than 4 cm may be candidates for percutaneous aspiration, or should undergo removal of the cyst because of a significant risk of torsion. Complex cystic masses, symptomatic ovarian cysts, and cysts that do not resolve should be removed.