Obesity has increased dramatically worldwide over the last two decades, becoming a social concern. In pregnancy, obesity is associated with increased risk of maternal death and of significant complications, such as pre-eclampsia, diabetes and postpartum hemorrhage. Several papers have also reported an increased risk of major anomalies in the offspring of obese pregnant women. At the same time, carrying out an ultrasound examination on an obese pregnant woman is a difficult task, due to the impaired acoustic window. This Review discusses the clinical, technical and medicolegal problems associated with ultrasound examination in obese and/or overweight women and provides tips for performing these examinations.