Chorioangioma is the most common tumor of the placenta. Since these tumors generally have small sizes, they cannot be detected during the routine ultrasonography (USG) examination and might not present any symptom. When they become larger in size, they can cause various maternal and fetal complications. We presented a patient whose obstetric USG examination revealed a placental mass compatible with chorioangioma and who had preterm delivery at the 34th gestational week. The size of the mass increased rapidly in last four weeks. The pathological examination indicated that the placental mass was 9x8 cm in size and compatible with angiomatous type chorioangioma.