Pneumopericardium complicating the course of hyaline membrane disease in a newborn, premature infant is reported. The details of other instances of neonatal pneumopericardium although unassociated with hyaline membrane disease are reviewed. The clinical manifestations, similar to those of pneumomediastinum, appear very suddenly and can lead to cardiac tamponade. Most cases described in the newborn infant are a complication of assisted ventilation by intermittent positive pressure. The chest x-ray characteristically shows a zone of diminished density surrounding the cardiac silhouette. The prognosis is bad unless emergency treatment (puncture and aspiration) is promptly performed.