Spontaneous mediastinal emphysema, an apparently uncommon disorder of children, is characterized by precordial pain, unusual crunching sounds heard over the precordium during auscultation, subcutaneous air palpable in the neck, and the presence of mediastinal air on the chest roentgenogram. CASE REPORT A 13-year-old male adolescent had worked all afternoon mowing lawns. When his gas-powered mower stalled, he restarted it by pulling the starter cord vigorously and frequently. After the evening meal, he clipped a hedge by hand. Within one hour, he developed severe substernal pain. He had a sense of substernal pressure. He felt "... as if I were going to explode," and thought he was having a heart attack.