Delafloxacin, like other fluoroquinolones, is associated with a low rate (3% to 4%) of serum enzyme elevations during therapy. These abnormalities are generally mild, asymptomatic and transient, resolving even with continuation of therapy. ALT elevations above 5 times the upper limit of normal occur in 1% or less of subjects. Although delafloxacin may not have been clearly linked to cases of clinically apparent liver injury, the other fluoroquinolones, such as ciprofloxacin, levofloxacin and moxifloxacin, rank among the 25 most common causes of drug induced liver injury in many case series. Estimates of the frequency of liver injury from fluoroquinolones have been 1:15,000 to 1:25,000 exposed persons. Delafloxacin has been in clinical use for a short time only, but is likely to have a similar frequency and pattern of liver injury as the other fluoroquinolones. The typical presentation of fluoroquinolone associated liver injury is with a short latency (1 day to 3 weeks) and abrupt onset with nausea, fatigue, abdominal pain and jaundice. The pattern of serum enzyme elevations can be either hepatocellular or cholestatic, cases with the shorter times to onset usually being more hepatocellular. In addition, the onset of illness may occur a few days after the medication is stopped. Many (but not all) cases have prominent allergic manifestations with fever and rash, and the liver injury may occur in the context of a generalized hypersensitivity reaction. Autoantibodies are usually not present. Most reported cases of liver injury from fluoroquinolones have been mild and self-limited, with recovery in 4 to 8 weeks from onset. However, the fatality rate of cases with jaundice has been greater than 10%. In addition, cases with a cholestatic pattern of serum enzymes may run a prolonged course and, in rare instances, have progressed to chronic vanishing bile duct syndrome leading to liver failure. Nevertheless, delafloxacin is a relatively recently introduced antibiotic and has yet to be convincingly linked to instances of acute hepatitis or jaundice. Likelihood score: E* (unproven but suspected cause of clinically apparent liver injury).