In this randomized, multicenter, observer-blind study, the efficacy, safety and tolerability of amoxycillin/clavulanate and cefaclor were compared in children with a clinical diagnosis of acute otitis media. Patients aged between 1 and 12 years received either amoxycillin/clavulanate (250 mg/62 mg t.i.d., or 125 mg/31 mg t.i.d. if aged under 6 years) or cefaclor (250 mg t.i.d., or 125 mg t.i.d. if aged under 6 years) for 7 days. The amoxycillin/clavulanate regimen was based on a dose of 20/5 mg/kg/day (representing 20 mg amoxycillin plus 5 mg clavulanic acid) in three divided doses. Patients were followed-up at the end of therapy and on days 10-12 and 38-40. At the end of the study (days 38-40), clinical success rates were 91.4% for amoxycillin/clavulanate and 78.6% for cefaclor. The difference was statistically significant (p = 0.008). After the 7 days of treatment, 3 patients (2.9%) in the amoxycillin/clavulanate group had clinical failure, compared with 18 patients (16.1%) in the cefaclor group (p < 0.001). Both treatments were well tolerated and there were no statistically significant differences between the groups in adverse event profiles. The incidence of diarrhea was low (7.0% amoxycillin/clavulanate, 8.4% cefaclor) and was generally of mild or moderate intensity. The study demonstrated that amoxycillin/clavulanate was significantly more effective clinically than cefaclor in the treatment of acute otitis media in children.