This multicentre, double-blind study was undertaken to demonstrate non-inferiority of once-daily oral moxifloxacin compared with combination therapy in the management of acute, uncomplicated pelvic inflammatory disease (PID). Women aged >or=18 years with PID were randomized to receive moxifloxacin (400 mg once daily) for 14 days or comparator treatment (doxycycline [100 mg twice daily] plus metronidazole [400 mg three times daily] for 14 days, plus one single 500-mg ciprofloxacin dose). Of the 434 valid per protocol (PP) patients, the overall clinical success rates at 2-14 days post-therapy were 96.6% (moxifloxacin) and 98.0% (comparator); moxifloxacin was non-inferior to the comparator regimen both in the PP (95% confidence interval [CI]: -4.5, 1.6) and intent-to-treat (95% CI: -5.8, 6.9) populations. Clinical success rates at 21-35 days post-therapy were 93.8% (166/177; data missing for 47 patients) for moxifloxacin and 91.3% (147/161; data missing for 37 patients) for the comparator. Bacteriological success rates at 2-14 days post-therapy were 92.5% (moxifloxacin) and 88.2% (comparator). Once-daily dosing and proven efficacy suggest that moxifloxacin may be of value in acute, uncomplicated PID.