The fluoroquinolone antibiotics sparfloxacin, grepafloxacin, gatifloxacin, and levofloxacin have been reported to cause torsades de pointes. Pre-existing risk factors increase vulnerability to this life-threatening arrhythmia. In a 65-year-old woman with a history of hypertension, coronary artery disease, systemic lupus erythematosus, and osteomyelitis, QTc interval prolongation (605 ms) and torsades de pointes developed after the initiation of levofloxacin, 250 mg intravenously once daily. The patient was hypokalemic and mildly hypomagnesemic before the initiation of levofloxacin and at the time of occurrence of torsades de pointes. The QTc interval decreased to 399 ms within hours of discontinuation of the levofloxacin, after which she had no further arrhythmias. In this and the majority of other published cases of fluoroquinolone-associated torsades de pointes, patients had at least 1 risk factor for the arrhythmia, and most had multiple risk factors. Fluoroquinolone antibiotics should be avoided whenever possible in patients with pre-existing risk factors for torsades de pointes.