External otitis is a common condition characterized by inflammation of external auditory canal and auricle. Topical agents used for treatment may cause contact dermatitis. In this article, we present a 48-year-old male patient admitted to our clinic with complaint of black colored lesions, pain, and discharge on his ear on third day after the start of gentamicin treatment by a primary health care unit due to a diagnosis of acute external otitis. In physical examination, we observed widespread skin necrosis on cartilage part of external auditory canal and cavum conchae. High resolution computed tomography of the temporal bone was performed with a prediagnosis of malignant external otitis. Ear culture and biopsy from the necrotic region were conducted. Intravenous piperacilline-tazobactam treatment was started. Upon normal results from radiologic and culture examinations, we considered a chemical reaction due to topical gentamicin application. Patient was discharged after debridement and wound care without any complications. Because of its high morbidity and mortality rates, malignant external otitis should be the first to eliminate in the differential diagnosis in patients that apply with widespread necrosis on external auditory canal and auricle and drug reactions that may cause the same clinical picture should not be ignored.