[A case of Hamman's syndrome associated with acute-onset type 1 diabetes mellitus presenting with abdominal pain].

: A 21-year-old female presented at an emergency department with abdominal pain and nausea. Computed tomography (CT) of the chest and abdomen revealed a small amount of mediastinal emphysema in the precardiac area, but the underlying cause could not be identified. On admission, her plasma glucose was 371 mg/dl, glycated hemoglobin (HbA1c) was 14.0%, and blood pH was 6.91. These findings supported a diagnosis of Hamman's syndrome associated with diabetic ketoacidosis. Her diabetic ketoacidosis was managed with insulin and fluid therapy, and the mediastinal emphysema disappeared spontaneously by the time of discharge. Presence of free air of the chest and abdominal cavity must warrant a differential diagnosis of gastrointestinal perforation; however, when the free air is accompanied by diabetic ketoacidosis, it is not necessary to perform urgent endoscopy.