A large yolk sac in a deformed shape gestational sac was detected by ultrasonography in an 8 week pregnant woman. The disappearance of the yolk sac and the gestational sac, enlargement of the uterine cavity and a heterogeneous appearance similar to early gestational trophoblastic disease were recognized when ultrasonographic examination was performed 2 weeks later. After uterine evacuation, partial hydatidiform mole was diagnosed by histopathological evaluation of the curettage material. In our study, the role of the large yolk sac in predicting trophoblastic disease is discussed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.