Anteroposterior supine chest radiograph in a 13-month-old preterm girl with a history of bronchopulmonary dysplasia, treated at a paediatric hospital because of acute viral respiratory infection, who presented with sudden respiratory failure. Black arrow points to the dense opacity in the right upper lung zone which was misdiagnosed as confluent atelectasis accompanying viral bronchiolitis. The lucent linear band along the right side of the heart (white arrow) and the lucent area in the lower mediastinum (asterisk) are possible CXR findings of pneumomediastinum; however, they were not correctly diagnosed on CXR. Interposition of air between the diaphragm and the heart, linear bands of air parallel to the left side of the heart or extension of air along the great vessels into the neck, which are among the more typical signs of pneumomediastinum, were not present on this CXR. Of note, mild left lower lobe atelectasis is also seen. CXR: chest radiography.