Pneumomediastinum in an infant is uncommon, and most literature on the subject is anecdotal or retrospective. Concurrent pneumomediastinum and pneumoperitoneum in an infant is even more unusual. We report the case of a 7-month-old infant with long-chain acyl-coenzyme A dehydrogenase deficiency who was admitted to the hospital because of respiratory failure and in whom radiographs revealed simultaneous pneumomediastinum and pneumoperitoneum. Benign findings at the abdominal examination and the presence of pneumomediastinum in the setting of assisted mechanical ventilation led to the diagnosis of air dissection syndrome. We review the radiographic findings associated with air dissection syndrome and discuss the management of concurrent nonsurgical pneumomediastinum and pneumoperitoneum in an infant.