Objective: To report an episode of diabetic ketoacidosis (DKA) in a patient with type 1 diabetes mellitus treated with low doses of neutral protamine Hagedorn insulin. The patient had recently initiated treatment with a sodiumglucose cotransporter-2 inhibitor as well. Methods: We describe the clinical presentation, laboratory data, and management of a diabetic patient with DKA. Results: A 50-year-old diabetic male presented with weight loss, fatigue, nausea, recurrent vomiting, muscle pain, malaise, and shortness of breath 2 weeks after initiation of empagliflozin and reduction in insulin dose. On admission to the emergency department, the glucose concentration was 541 mg/dL, pH 7.087, bicarbonate 4.5 mmol/L, blood urea nitrogen 50 mg/dL, creatinine 2.0 mg/ dL, and beta-hydroxybutirate 4.1 mmol/L. The estimated osmolality was 319.9 mOsm/L and the anion gap was 25.6 mEq/L. Empagliflozin was discontinued; the patient was treated with balanced electrolyte solutions and continuous insulin infusion with resolution of acute kidney injury and metabolic acidosis. C-peptide level was <0.1 ng/mL and anti-glutamic acid decarboxylase-65 was 6 IU/mL (reference range is <5 IU/mL). Conclusion: In this patient, who was misdiagnosed with type 2 diabetes mellitus, the insulin dose reduction provoked DKA. When selecting sodium-glucose cotransporter-2 inhibitors in diabetics, physicians must assure adequate insulin provision as well as strict monitoring of blood glucose and urine ketones. (AACE Clinical Case Rep. 2018;4:e505-e508) Abbreviations: DKA = diabetic ketoacidosis; NPH = neutral protamine Hagedorn; SGLT2 = sodium-glucose cotransporter-2; T1DM = type 1 diabetes mellitus; T2DM = type 2 diabetes mellitus e506 DKA in T1DM with SGLT2 inhibitor, AACE Clinical Case Rep. 2018;4(No. 6)