Pneumomediastinum can result from a puncture wound or laceration to the hypopharynx. This is a case report of an 18-month-old child who fell with a pen in his mouth. Initial physical examination was unremarkable, but the child developed neck swelling, fever, and irritability over the next 12 hours. Repeat examination revealed marked pneumomediastinum and subcutaneous emphysema. The pathophysiology and treatment of pneumomediastinum are reviewed.