Since it is relatively rare, spontaneous pneumomediastinum is often little known to clinicians. Making the diagnosis, however, presents no problem if the three essential signs are present, that is to say: -subcutaneous emphysema of the base of the neck (7 cases), -Hamman's sign, (6 cases), -a paramediastinal air shadow on chest roentgenograms, (8 cases). The condition is brought about by rupture of perivascular alveoli resulting in the migration of air along the pulmonary vessels. The principal advantage of making the diagnosis is that it enables one to eliminate other pain-causing thoracic syndromes, especially myocardial infarction, pulmonary embolus and acute pericarditis. The clinical course is usually benign necessitating no treatment.