Reports of neonatal ovarian cysts are few, partly because only large tumors, or tumors causing complications, have been diagnosed clinically in the past. The early diagnosis of cystic intraabdominal masses in the fetus was accidental before the introduction of ultrasonic screening examinations for the gravid population. Consequently, there was no adequately documented basis for discussing their real frequency, differential diagnosis, follow-up, and therapy. The present case report is put forward in order to elucidate the diagnostic and therapeutic problems associated with ovarian cystic masses in the fetus. A routine ultrasonic examination with real-time equipment was performed on a 29-year-old woman, gravid 2, at the 39th week of pregnancy. A single fetus with relatively large head and body diameters (biparietal diameter, 10.0 cm; transverse abdominal diameter, 11.2 cm) was verified in breech presentation. Transverse examination of the lower abdomen of the fetus revealed two large cystic masses on either side of a medially located cystic structure, which was thought to represent the urinary bladder. The diameters of the cysts were 6 cm (right) and 2.5 to 3 cm (left). Both kidneys were normal in size, shape, and location. A detailed ultrasonic examination of the fetus showed no other abnormalities, and the tumor finding remained constant. An elective cesarean section was performed 5 days after admission because of the relatively narrow pelvis, the breech presentation, and the strong suspicion of large ovarian cysts in the fetus. The newborn girl weighed 3910 g and had Apgar scores of 9 at one minute and 9 at five minutes. A soft resistance was felt in the lower right quadrant upon abdominal palpation. An ultrasonic examination of the infant, carried out at the age of 2 days, showed normal kidneys on both sides, with a slightly enlarged renal pelvis on the right. Two cystic structures (diameters, 6 cm on the right and 3 cm on the left) were diagnosed in the lower abdominal area. Intravenous urography was performed 2 days later. The excretion from the kidneys was symmetrical, and no tumor formations were observed in the areas of the kidneys or ureters. When the palpable tumors in the abdomen remained unchanged at the age of 8 days, a laparotomy was performed because of the risk of complications from such large tumors. Large cystic tumors originating from both ovaries were found, with diameters approximately 6 cm (right) and 4 cm (left). Both of these were excised macroscopically from the ovaries, great care being taken to leave the main ovarian structures intact on both sides. Both cysts were uni-locular and contained a serous yellow fluid. Histopatho-logical examination showed the insides of the cysts to be lined with theca-lutein cells of a benign character. Immediate recovery was good, and the condition of the child at the age of a month-and-a-half was excellent.