Introduction. Pneumomediastinum is defined as the presence of free air in the mediastinum. Primary, idiopathic, spontaneous pneumomediastinum is very rare and it affects healthy children with no identifiable cause. Secondary pneumomediastinum may be caused by underlying respiratory disorders, iatrogenic causes or trauma. The most common clinical sign of pneumomediastinum is subcutaneous emphysema, and the most common symptoms are acute chest pain and dyspnea. The diagnosis is confirmed by a chest X-ray or chest computed tomography. Pneumomediastinum is rarely associated with pneumothorax, pneumoperitoneum, and pneumorrhachis. Case Report. In this report, we present a case of a spontaneous pneumomediastinum in a child aged 2 years and 6 months. A child was admitted to our hospital due to massive subcutaneous emphysema. On admission, the patient was without a history of chest trauma or any chronic respiratory tract diseases. He had a mild upper respiratory tract infection 6 days before admission. The diagnosis of pneumomediastinum was confirmed by chest X-ray and computed tomography. After conservative treatment, on the eighth day of hospitalization, there was a complete regression of the pneumomediastinum with normalization of the clinical and radiological findings. Conclusion. Spontaneous pneumomediastinum is the most common benign condition that spontaneously regresses after conservative treatment. Life-threatening complications require surgical decompression. The use of antibiotic therapy in the prophylaxis of mediastinitis has not been proven to be useful. Opinions on the routine use of chest computed tomography in patients with spontaneous pneumomediastinum are still not uniform.