Vasa previa, which is associated with high fetal mortality, is present when fetal vessels cross the internal cervical os as a velamentous insertion of the umbilical cord with or without a succenturiate lobe or bilobate placenta. This is the first case report of vasa previa not associated with a succenturiate lobe or bilobate placenta and in which the diagnosis was made using a combination of transvaginal ultrasonography and color flow Doppler ultrasound. The infant was delivered by elective cesarean, and the ultrasound findings were confirmed. Color flow Doppler and transvaginal ultrasound facilitate this diagnosis because the internal os and surrounding structures are easier to visualize; in addition, vascular flow and Doppler patterns characteristic of the umbilical cord can be demonstrated in structures suspected to be vessels.