Diabetic Ketoacidosis (DKA) is the most common metabolic complications of diabetes mellitus. In some situations, other acid-base disorders coexist with DKA including metabolic alkalosis. There is several underlying etiology for the DKA with metabolic alkalosis such as extracellular volume loss secondary to vomiting or diuretics, alkali ingestion, and corticosteroid excess. We report herein the first case of DKA with metabolic alkalosis secondary to autopsy-confirmed Cushing disease. The case report elucidates clinically important lessons through its management as well as a future guide for scientific investigation on this combined acid-base disorder.