We have reported a rare case of a giant ovarian tumor which, due to the lack of proper health care on the side of the patient, had not been diagnosed until 27 weeks of pregnancy. The patient did not demonstrate any clinical symptoms till the moment of the diagnosis. Peripheral blood analysis showed severe anemia at the admission. The right adnex with the multilocular cystic tumor containing bloody fluid and measuring 40 cm in diameter, was removed in the course of the surgical procedure. The histological diagnosis of the tumor was: serous cyst. Surgical removal of the giant tumor allowed for further development of pregnancy and enabled vaginal delivery of healthy newborn at term.