The debate over the application of nuchal translucency measurement in Down's syndrome screening is still unresolved in some clinicians' minds. Although different authors report a range of sensitivities for Down's syndrome, none question the validity of the association between increased nuchal translucency and fetal aneuploidy. The published literature reveals a lack of congruence over a standard, reproducible method for measuring nuchal translucency. Only with the adoption of uniform methodology, and the establishment of international standards for nuchal translucency measurement, is the true potential of this test likely to be realized. The increasing use of first trimester ultrasound has focused attention on the value of this investigation in confirming fetal viability, estimation of gestational age, and screening for congenital abnormality. This review summarizes the role of ultrasound and maternal serum biochemistry in first trimester screening.