This report describes a rare case of perioperative midazolam hypersensitivity in a patient without any history of allergy. A 39-year-old man was admitted for endoscopic pansinus surgery. During transportation to the operating room after injecting antibiotic and midazolam intravenously, the patient complained of shortness of breath. At 3 months after the event, an intradermal sensitivity test for midazolam proved positive indicating the incident was caused by midazolam hypersensitivity.