An 18-year-old male with type 1 diabetes mellitus presented to the emergency department after one day of lethargy and vomiting. Physical examination revealed a dehydrated male with tachycardia and Kussmaul's respiration. There was subcutaneous emphysema in both supraclavicular regions. Chest auscultation revealed a positive Hamman's sign. Laboratory investigation was significant for metabolic acidosis with venous blood pH 7.08. Plasma glucose was 1438 mg/dl; ketones were present in the urine. Chest X-ray showed subcutaneous emphysema and pneumomediastinum, which resolved spontaneously within 72 hours of initiation of treatment for diabetic ketoacidosis.Pneumomediastinum is an uncommon complication of diabetic ketoacidosis. Recognizing that severe diabetic ketoacidosis may cause pneumomediastinum allows for expedient management.