The antenatal diagnosis of congenital heart disease by fetal echocardiography is rarely achieved before 18-20 weeks' gestation. Transvaginal sonography allows examination of fetal anatomy at earlier gestations than the transabdominal approach. In a screening study of 270 low-risk women between 8 and 14 weeks' gestation using a 5 MHz vaginal transducer, it was possible to obtain adequate four-chamber views in over 70% from 12 weeks. In a second study of 32 women at high risk of congenital heart disease scanned between 14 and 15 weeks' gestation, satisfactory views were obtained transvaginally in 21 women. Seven of the remainder had normal cardiac anatomy confirmed by transabdominal scanning. In three of the four where normal cardiac anatomy could not be demonstrated by either transvaginal or transabdominal scanning, severe congenital heart disease was diagnosed and later confirmed. It is unlikely that transvaginal sonography will replace abdominal scanning for the screening of low-risk pregnancies, but it is a valuable addition to the early examination of those women identified as being at high risk of congenital heart disease.