OBJECTIVE To evaluate the role of ultrasound in the diagnosis and prediction of the clinical course of a large chorioangioma. METHODS Six women with a large chorioangioma were consecutively detected at 26 28 weeks gestation by ultrasound. At initial examination, the tumors were evaluated for size, vascularity, location, and echogenecity (relative to placenta). Fetuses were assessed anatomically and for early signs of hydrops. Sonographic fetal and tumor examination were repeated weekly until delivery, and associated maternal complications were recorded. RESULTS The sonographic diagnosis of chorioangiomas was subsequently confirmed pathologically in all cases. The maximum diameter of the tumors varied between 6 and 12 cm. Chorioangioma was hyperechogenic, avascular and complicated by intrauterine fetal growth restriction and oligohydramnios in one woman; a healthy but small for date infant was delivered at 38 weeks gestation. Two tumors were partially vascular and hyperechogenic, these tumors were associated with moderate polyhydramnios and preterm delivery of normal infants at 33 and 36 weeks. The remaining 3 tumors were hypoechogenic, diffusely vascular and were associated with severe polyhydramnios. In one case, the tumor was complicated by abrupt generalized non immune fetal hydrops and stillbirth; in the 2nd case, there was acute fetal distress and delivery of a premature anemic infant at 28 weeks; however, in the 3rd case, while the polyhydramnios and tumor vascularization decreased, its echogenecity increased and delivery of normal infant at full term was achieved. CONCLUSION Sonographic assessment of echogenicity and vascularity of the large chorioangioma appears to be detrimental in predicting the clinical outcome of pregnancy. Spontaneous regression of tumor vascularity with subsequent resolution of hydramnios may occur. While vascular and hypoechogenic tumors are associated with higher incidence of pregnancy complications, favorable outcome is expected in avascular and hyperechogenic tumors.