- Pneumomediastinum is characterized by the presence of air in the mediastinum and has been recognized since 1827, when described by Laënnec. To the best of our knowledge, pneumoperitoneum as a result of spontaneous pneumomediastinum has not yet been described in the English literature. We observed and treated a young patient in the intensive care unit who presented with spontaneous pneumomediastinum. Free intra-abdominal gas was observed on the chest x-ray film on the day after admission. Management was conservative. Intra-abdominal and mediastinal air disappeared within four days. This condition, when recognized, needs only observation; we report this as a medical curiosity.