We analyze the potential use of ultrasound in the study of the thorax in children. The physical limitations imposed on sonography by the ventilated lung and thoracic cage are well known. We want to discuss new US applications based on the clinical and methodological experience gained in adults as outlined by emergency and critical care specialists. These specialists take information from physical acoustic phenomena that is not directly convertible into images of the human body, starting with the interpretation and handling of artifacts. We give a critical assessment from a radiologic viewpoint that is both necessary and important.