A 63-year-old woman presented to our hospital with a 13-day history of nonproductive cough that had progressively worsened. She was quite hypoxemic, and her chest computed tomography revealed diffuse ground-glass opacities in both lungs. She had type 2 diabetes mellitus and had been taking sitagliptin 16 days earlier. Stains and cultures of bronchoscopic specimens for bacteria, fungi, and acid-fast bacilli were negative; moreover, all other infectious examinations were also negative. Thus we diagnosed her as drug-induced lung injury with sitagliptin by positive response to a drug-induced lymphocyte stimulation test. Although she required mechanical ventilation for progressive respiratory failure a day after admission, she was recovered within a couple of days soon after an initiation of treatment with prednisolone. The dipeptidyl peptidase-4 (DPP-4) inhibitors are widely adopted in diabetes mellitus therapy. It should be noted that DPP-4 inhibitors may cause lung injury.