We report a case of a 29-year-old woman who is known to have systemic lupus erythematosus and idiopathic interstitial pneumonia; she presented with a 1-day history of substernal chest pain and increasing shortness of breath. On examination, she was found breathless, but was not distressed or afebrile or normotensive. Auscultation of the heart revealed a positive Hamman's sign. There was chest-wall crepitus, and auscultation of the lung showed bilateral crepitations. Full blood count and biochemical profile were unremarkable. Chest x-ray showed signs of idiopathic interstitial pneumonia in addition to pneumomediastinum (linear band of air within mediastinal planes and continuous diaphragm sign) and chest-wall subcutaneous emphysema. She was treated with high-concentration oxygen. A repeat chest x-ray 5 days later showed complete resolution of the pneumomediastinum and subcutaneous emphysema, but signs of idiopathic interstitial pneumonia continued to persist.