Fetal echocardiography can be used to detect congenital heart disease prenatally with a high degree of accuracy, and complex heart malformations have also been clearly described in the fetus. However, it is difficult to diagnose correctly or to exclude definitely aortic coarctation by fetal echocardiography. A 23-year-old woman was referred for fetal echocardiographic examination at 21 weeks' gestation after discovery of hydrops fetalis (nonimmune) on an obstetric ultrasound examination. Aortic isthmus appeared hypoplastic with a diameter < or = 3rd percentile for gestational age. There was a narrowing within the descending aorta immediately distal to the origin of the ductus arteriosus. Color flow imaging demonstrated acceleration and turbulent flow and the peak pressure gradient was measured 83 mmHg by continuous wave Doppler in the same area. The pregnancy terminated in spontaneous abortion at 22 weeks' gestation. The fetus was stillborn. The autopsy findings confirmed the prenatal diagnosis. We conclude that together with the quantitative estimation of the aortic arch, color Doppler and continuous wave Doppler are helpful in diagnosis and estimation of the pressure gradient.