We report a case of spontaneous pneumomediastinum (SPM) in a 3 year-old child, admitted to the emergency department because he presented dyspnea for a few hours, after a paroxysm of cough. The SPM is rare in children; the term "spontaneous" is reserved for cases of pneumomediastinum that haven't a traumatic cause. SPM is seen most commonly in asthmatics and in any patient who induces a Valsalva maneuver. The clinical diagnosis is confirmed by chest radiograph. When the diagnosis is uncertain, the chest CT scan is considered the gold standard of imaging tests, capable of detecting pneumomediastinum even in patients with small amounts of mediastinal air. In this case CT images showed the cause: spontaneous bronchial rupture. The direct sign of bronchial injury is the contiguity of the luminal air with that in the mediastinum. In the literature SPM cases are very rare, at least in health patients without tracheobronchial anomalies. The SPM is generally a benign entity that requires supportive care, and resolution occurs spontaneously, such as in our patient. In this article we want to explain the main clinical, diagnostic and therapeutic aspects of SPM, because, even if it's rare in children, it must be considered in the differential diagnosis of dyspnea; then we want to demonstrate as, in this case, a TC scan was important to identifying the SPM cause: a bronchial rupture.