The incidence, aetiology and pathophysiology of pneumomediastinum (PM), an uncommon and potentially serious disease in neonates and children were evaluated. A retrospective chart review of all patients diagnosed with PM who were hospitalized in the intensive care unit of the University Children’s Hospital Zurich, Switzerland, from 2000 to 2006, was preformed. We analysed the incidence, severity and causes of PM, and investigated possible differences between neonatal and non-neonatal cases. Seven children and nine neonates were identified with PM. All patients had a good outcome. Six cases of PM in the group of children older than 4 weeks were deemed to be caused by trauma, infection and sports whereas one case was idiopathic. All nine neonatal cases presented with symptoms of respiratory distress. We were able to attribute four cases of neonatal PM to pulmonary infection, immature lungs and ventilatory support. Five neonatal cases remained unexplained after careful review of the hospital records. In conclusion, PM in children and neonates has a good prognosis. Mostly, it is associated with extrapulmonary air at other sites. It is diagnosed by chest x-ray alone. We identified mechanical events leading to the airway rupture in most children >4 weeks of life, whereas we were unable to identify a cause in half of the neonates studied (idiopathic PM).