At the time of writing, the accuracy of ultrasound in detecting fetal anomalies remains a subject of debate in the literature. Fetal ultrasound is clearly the com­bination of sophisticated technology and skilled medical craftsmanship, strictly intertwined. The ability to detect fetal anatomical defects depends largely upon the operator's skills and expertise. It is clear that despite the quality of instru­mentation and the ability of the operator, a reasonable proportion of fetal anoma­lies will be missed. The remarkable results of pilot studies performed in referral centres are largely due to the selection of patients. Such studies include large numbers of pregnancies in which either a fetal anomaly had been previously suspected during a basic scan or there was a family history of anomalies ame­nable to ultrasound diagnosis. Independently from the expertise of the operator or the equipment used, some fetal anomalies will not be detectable in utero or in early gestation due to either late development or limitations of current ultra­sound technology. Examples of the former group of lesions include persistence of the fetal circulation, disruptions (porencephaly, migrational disorders), tumours, intestinal obstructions, urinary tract dilation and many types of skeletal dyspla­sias. Examples of the latter group include ventricular and atrial septal defects. Given the heterogeneity of congenital anomalies, in many cases it remains diffi­cult to establish whether a specific condition can be recognized in early gestation or not. Indeed, even within the same centre indicated sonograms result in a much greater sensitivity than screening examination performed on low-risk patients.