© 2018 Elsevier Inc. All rights reserved. Noonan syndrome is a disorder characterized by specific facial dysmorphisms, cardiovascular defects, short stature, and variable developmental delay. Noonan syndrome should be suspected prenatally in any fetus with cystic hygroma and normal karyotype, especially if a congenital heart defect is noted (particularly pulmonary stenosis). Because of the overlap between features of Noonan syndrome and other genetic disorders, postnatal physical examination in addition to molecular testing may be necessary for proper diagnosis. Noonan syndrome is genetically heterogeneous; it is mostly inherited in an autosomal dominant manner with complete penetrance and variable expressivity. Prenatal sonographic findings do not predict postnatal phenotype of Noonan syndrome. Life expectancy among patients with Noonan syndrome and minor cardiac anomalies is normal.