Spontaneous pneumomediastinum is a relatively rare disease, the clinical signs of which may be misleading, and the physiopathology is still unknown. The authors report 7 cases collected over a period of 3 years and note the etiology, the clinical findings and the X-ray findings. The disease often affectsyoung sybjects, without any sex predominance. The initial symptom is thoracic pain and is often accompanied by dispnea. Subcutaneous emphysema only appears secondarily and may be mild. The association with pneumothorax is not rare. Among the etiological circumstances, pneumomediastinum often occurs after an effort or a respiratory infection with dyspnea. The diagnosis depends on the discovery of subcutaneous emphysema and on radiological signs in A.P. and lateral chest views. Treatment should be as conservative as possible in the usual benign forms. It should be limited to bed rest, analgesics and sedatives. In severe cases, supra-sternal drainage permits decompression of the mediastinum. The physiopathological mechanisms are discussed, but the usually accepted theory is rupture of an alveolus into the pulmonary interstitial tissue. The pressure gradient necessary for this rupture may be due to variations in alveolar or vascular pressure.