The efficacy and safety of amoxycillin/clavulanic acid (AMX/CA) (875/125 mg b.i.d. for 14 days) were compared with that of cefuroxime axetil (500 mg b.i.d. for 14 days) in a multicenter, open, parallel-group, randomized clinical trial in 206 adults with chronic or acute exacerbation of chronic sinusitis. Clinical response was similar, with 95% of AMX/CA-, and 88% of cefuroxime-treated, clinically evaluable patients cured (95% confidence interval; -0.6% to +15%). In bacteriologically evaluable patients, cure rates, defined as eradication of the original pathogen with or without re-colonization with non-pathogenic flora, were also similar, with 65% of AMX/CA- and 68% of cefuroxime-treated patients cured (95% confidence interval; -18% to +15%). However, clinical relapse was significantly higher in the cefuroxime group: 7% (7/89) of clinically evaluable patients, compared with 0% (0/98) in the AMX/CA (p=0.0049) group. A similar incidence of possible or definite adverse events related to the study drug was reported for both treatments (AMX/CA 4.4%, cefuroxime 4.3%), the most frequent being diarrhea. Four adverse events were recorded as serious or life-threatening with only one considered related to the study drug (urticaria, cefuroxime). AMX/CA 875/125 mg b.i.d. for 14 days is as effective and well tolerated as cefuroxime axetil 500 mg b.i.d. for 14 days in the treatment of chronic, or acute exacerbation of chronic sinusitis, but is associated with a significantly lower clinical relapse rate.