This paper reviews the safety data for levofloxacin utilizing reports from clinical and post-marketing surveillance trials. The side effect incidence rates are 1.3% for nausea, 0.1% for anxiety, 0.3% for insomnia, and 0.1% for headache. No levofloxacin-related adverse events were reported at a rate higher than 1.3%, and most were lower. Four clinical trials were reported. Levofloxacin achieved superior clinical and microbiological results compared to ceftriaxone/macrolide combination, and was better tolerated. Results comparing IV azithromycin plus ceftriaxone versus 500 mg levofloxacin in hospitalised CAP demonstrated that levofloxacin performed better, with more adverse events associated with the comparators (levofloxacin 5.3%, comparators 9.3%). High-dose levofloxacin (750 mg) was also evaluated and found to be well tolerated. Surveillance data reported low ADR rates for levofloxacin: nausea 0.8%, rash 0.5%, abdominal pain 0.4%, and diarrhoea, dizziness, and vomiting 0.3%. Worldwide and US surveillance data confirmed that tendon rupture occurred in less than 4 per million prescriptions, taste perversion in less than 3 per million, convulsions in 2 per million, and photosensitivity, hepatitis, hepatic failure, QT prolongation, torsade de pointes or empyema all in less than 1 per million. Copyright 2001 S. Karger AG, Basel