Objectives: To illustrate how Apert syndrome, a rare autosomal dominant genetic syndrome, can be detected in the second-trimester of pregnancy using 2D ultrasound, and how 3D ultrasound examination may provide parents with a better understanding of the structural defects affecting their baby. Methods: Fetal Medicine Unit database searches to identify Apert syndrome cases. Results: Five cases of Apert syndrome were suspected in the second-trimester when sonography showed abnormal extremities including syndactyly, and an abnormal skull shape. In 1 case there was increased nuchal translucency with a normal fetal karyotype in the first-trimester. In all cases, a mutation of the FGFR2 gene confirmed the diagnosis of Apert syndrome. 3D ultrasound was used to show parents the extent of the abnormalities of the skull, face and extremities. Parents were counseled by craniofacial surgeons and geneticists. Conclusion: Apert syndrome can be accurately suspected in the second-trimester by careful ultrasound examination of the fetus including the extremities and skull shape. 3D ultrasound can be a useful adjunct to 2D examination for parental counseling. Copyright © 2007 John Wiley & Sons, Ltd.