ABSTRACT: Objective: Cushing syndrome (CS) is very rare in pediatric patients. The major cause of endogenous CS is Cushing disease (CD), which is due to excessive adrenocorticotropic hormone (ACTH) secretion from pituitary cells. CS that presented with diabetic ketoacidosis (DKA) has rarely been reported in adults. Methods: A case report and literature review. Results: A 12-year-old female suffering from polyuria and polydipsia for 3weeks was admitted with amenorrhea. Due to her hyperglycemia, ketonuria, glucosuria, and metabolic acidosis on arterial blood gas, she was diagnosed with DKA. Oral moniliasis, acanthosis nigricans, moon face, central obesity, and striae were detected on physical examination. Based on the results of overnight and low-dose dexamethasone suppression tests, the patient was diagnosed with CS. In a high-dose dexamethasone suppression test (HDDST), her urinary free cortisol (UFC) excretion rate was suppressed by 71.3%. Brain magnetic resonance imaging (MRI) revealed a 3-mm pituitary microadenoma. Because serum cortisol and24-hour UFC levels were not sufficiently suppressed by the HDDST and the diameter of adenoma in the MRI was <5mm, bilateral inferior petrosal sinus (BIPS) sampling was performed. A diagnosis of CD was confirmed by determining a high central/peripheral ACTH ratio of 11. Conclusion: Although very rare in childhood, CS should be considered in pediatric patients with obesity, acanthosis nigricans, moniliasis, and striae. DKA may be the presenting clinical feature in patients with impaired glucose metabolism.