An 81 years old man with known temporal arteritis who has been taking azothiopurine was admitted to our clinic with the complaint of changes in his fingernails. He was treated with intravenous levofloxacin for pneumonia 2 months before the nail change. A skin rash developed on the 5th day of treatment and resolved spontaneously in 1 week. Two months later, nail deformity started to develop. Dermatologic examination revealed onychomadesis, beau lines, yellow discoloration, subungual hyperkeratosis and erythema in the perineum of the nails of the hands and feet. Many drug classes have been associated with drug-induced nail abnormalities. Onychomadesis describes the presence of a transverse whole-thickness sulcus that divides the nail into 2 parts. Onychomadesis represents the extreme degree of Beau’s lines and shares the same pathogenesis, which a temporary arrest of nail matrix mitotic activity. Local trauma to the nail bed is the most common cause of single-digit onychomadesis. In our case, there was no systemic or dermatologic disease in the etiology of onychomadesis. Onychomadesis developing after quinolone group antibiotherapy was diagnosed with the patient’s medical history and dermatologic examination. Drug-induced nail abnormalities are usually transitory and disappear with drug withdrawal, but sometimes persist in time.