Screening for fetal anomalies by an ultrasound scan was introduced in many maternity units in the UK in the late 1970s and has become routine in most since then although there is little uniformity as to how the scan is performed and when it is offered. Up to 5% of babies are born with a congenital abnormality. In this review article we will focus on what is already known about screening for the commonest and most serious structural fetal anomalies at the 11-14 and 18-23 week scans, and discuss new techniques that promise to improve the accuracy of screening and diagnosis. Chromosomal abnormalities, "soft markers" and biochemical screening are beyond the scope of this review.