An 85-year-old woman with diabetes mellitus was admitted to our hospital due to progressive dyspnea. Two months previously, pioglitazone had been newly prescribed for diabetes management. Bilateral ground-glass opacities and progressive respiratory deterioration suggested respiratory failure due to a drug-induced lung injury. With discontinuation of pioglitazone and the administration of a corticosteroid, an improvement in her respiratory condition was achieved, although sequelae remained in some areas of the lungs. Results of drug-induced lymphocyte stimulation tests were positive for pioglitazone. Resumption of other drugs did not reinduce the lung injury. Therefore, a diagnosis of pioglitazone-induced lung injury was made. Although pioglitazone-induced lung injury is very rare, clinicians should keep it in mind when pioglitazone is used.