In the 17,108 patients receiving a fluoroquinolone or ceftriaxone, the rate of dysglycemia was greater in those receiving levofloxacin or gatifloxacin than in those receiving ceftriaxone. However, no difference was noted in the rate of glucose abnormalities with levofloxacin versus gatifloxacin. Clinicians should be aware of dysglycemic events that may occur in patients receiving fluoroquinolones, especially in those with diabetes mellitus or those receiving sulfonylureas.