Spontaneous pneumomediastinum (defined by the presence of free air in the mediastinum) is an infrequent entity that is presented in the absence of diseases or precipitating factors. It generally affects young and healthy males. Thoracic pain, dyspnea, or both, are the most frequent symptoms. Other signs and symptoms are subcutaneous emphysema and Hamman's sign. Simple radiography of the thorax allows for the diagnosis in a high percentage of patients. Conservative treatment is indicated in these patients and has a favourable prognosis. Relapses are infrequent.