Pneumomediastinum[Mediastinal emphysema is characterized by the presence of air in the mediastinum, and classified as spontaneous[occurring without obvious cause or secondary[caused by a trauma or artificial ventilation . To study the clinical evaluation of pneumomediastinum, data were obtained from 20 patients. The incidences of spontaneous pneumomedisastinum were 5 and those of secondary pneumomedistinum were 15 cases. The mean age was 21.2$pm$3.4 years[$pm$SD in spontaneous pneumomediastinum and 44.1$pm$20.0 years[$pm$SD in secondary pneumomediastinum. There were 16 male and 4 female patients. The common presenting compliants were retrosternal pain in 19 patients[95% , dyspnea in 12[60% , and hoarsness in 2[10% . The predisposing factors were asthma,excessive exercise and vomiting in spontaneous pneumomediastinum;trauma, artificial ventilation, tracheostomy, the rupture of trachea or esophagus in secondary pneumomediastinum. The physical findings were subcutaneous emphysema in 17 patients[85% , Hamman`s sign in 11 patients[55% and decreased cardiac dullness in 2 patients[10% . Spontaneous pneumomediastinums were managed conservatively, however, surigical procedures were needed in secondary pneumomediastinums. There was no recurrence, but one patinet died of tension pneumomedistinum. We concluded that spontaneous pneumomediastinum is uncommon, usually benign, and self-limited and secondary pneumomedistinum due to trauma or artificial ventilation is more increasing, and necessitates the early, aggressive intervention.