In this multicentre, multinational, comparative, double-blind clinical trial, out-patients with both symptoms and radiographic evidence of acute sinusitis were randomly assigned to receive either a seven-day, once daily (o.d.) oral regimen of moxifloxacin (400 mg) or a 10-day o.d. oral regimen of trovafloxacin (200 mg). Among 452 patients considered valid for clinical efficacy, moxifloxacin treatment was found to be statistically equivalent to trovafloxacin (96.9 per cent vs 92.1 per cent -95 per cent CI = 0.6 per cent; 8.9 per cent) at the seven to 10 days post-therapy assessment. At follow-up, the success rate in the moxifloxacin group was 94.9 per cent and that for the trovafloxacin group was 97.6 per cent (95 per cent CI = -4.9 per cent; 1.3 per cent). The predominant causative organisms were Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus followed by Enterobacteriaceae and Moraxella catarrhalis. The bacteriological success rate at the post-therapy evaluation was similar in both treatment groups: 94.4 per cent and 90.1 per cent in the moxifloxacin and trovafloxacin groups respectively (95 per cent CI = −3.0 per cent; 11.9 per cent). Only three of the 103 baseline isolated pathogens still persisted in the moxifloxacin group, whereas there were 10 of the 121 isolates that failed to respond in the trovafloxacin treatment group. At least one drug-related event was reported by 16.9 per cent of the moxifloxacin-treated patients and by 22.3 per cent of those who received trovafloxacin. CNS events such as dizziness and vertigo were reported more than five times more often in patients receiving trovafloxacin than in the moxifloxacin group. Trovafloxacin recipients were also more than twice as likely to discontinue treatment due to adverse events than moxifloxacin-treated patients. Overall, moxifloxacin was at least as effective clinically and bacteriologically as trovafloxacin and better tolerated.