Acute suppurative mediastinitis is an uncommon, life threatening condition with a mortality rate of up to 40%. It is mainly caused by esophageal perforation or post-operative complications, and acute mediastinitis not caused by trauma or surgery is rare. To the best of our knowledge, no cases of spontaneous mediastinal abscess in children have been reported in the English medical literature. We report here on a case of an acute mediastinal abscess in a ten-year-old girl and there was no demonstrable clinical or radiologic etiology for infection.