Objective: To define sonographic criteria that may improve the prenatal diagnosis of Noonan syndrome by targeted DNA testing. Methods: We searched our Fetal Medicine Unit records for all cases with a final diagnosis of Noonan syndrome. A literature review was undertaken to identify the sonographic features of Noonan syndrome fetuses. Information was pooled to define the most common features. Results: In our database, we identified three cases of Noonan syndrome. The diagnosis was suspected prenatally in two of them. Thirty-nine cases were identified in the literature. In the presented cases we show that suspicion of Noonan syndrome should arise when, after an increased nuchal translucency, ultrasound investigation in the second trimester shows a persistant nuchal fold (NF) or cystic hygroma in combination with at least one of the following features: hydrops fetalis, pleural effusion, cardiac anomalies, polyhydramnios or specific facial abnormalities. Conclusion: Prenatal ultrasound findings in Noonan syndrome can be subtle and aspecific, but when specific characteristics are present additional targeted DNA analysis is indicated. © 2011 John Wiley & Sons, Ltd.