Pneumomediastinum, which can be spontaneous or secondary, is defined by the presence of free air in the mediastinum as shown on a chest X-ray and/or chest CT, with or without subcutaneous emphysema. Secondary pneumomediastinum develops in various contexts (thoracic traumatism, perforation of central airway or digestive tract, pneumothorax, barotraumatism complicating mechanical ventilation…). Spontaneous pneumomediastinum , which will be the focus of this review, develops without any of the above-mentioned conditions.Spontaneous pneumomediastinum is a rare entity which usually occurs in young people either without medical history or with an history of asthma. A trigger event is detected in 40% to 60% of cases. Positive diagnosis is made on chest radiographt but thoracic CT is more sensitive. Distinction between spontaneous pneumomediastinum and secondary pneumomediastinum is in general easy but may sometimes be more difficult, particularly in case of oesophageal perforation. The evolution of spontaneous pneumomediastinum is most often benign but, rare complications may occur. Management is most often conservative.There is no consensual management of spontaneous pneumediastinum because of the lack of randomized prospective studies. This may be explained by the rarity of the disease. The actual trend is to offer to the patients a conservative treatment, which could be ambulatory in some cases.Spontaneous pneumomediastinum is a rare entity developing mainly in young subjects. The evolution is in general benign, justifying a conservative approach.