BACKGROUND: Compared with 5 days of dosing, a 3 day dosing regimen of azithromycin for treatment of acute otitis media (AOM) may improve compliance, will simplify therapy for the caregiver and, by giving the same total dose as the 5 day regimen, provide more drug when the bacterial burden is highest. METHODS: Children of 6 months-12 years were enrolled if they had had symptoms and signs of AOM for <4 weeks and tympanic membrane effusion by acoustic reflectometry. Eligible children were randomized to azithromycin 10 mg/kg/day x 3 days or co-amoxiclav 45 mg/kg/day x 10 days. The primary endpoint was clinical response at day 28. RESULTS: One hundred and eighty-eight children (mean age 3.5 years) were randomized to azithromycin and 185 to co-amoxiclav. At day 10, the clinical success rate was 153/185 (83%) in children treated with azithromycin and 159/181 (88%) in children treated with co-amoxiclav. At day 28, 134/182 (74%) of the children were cured on azithromycin compared with 124/180 (69%) on co-amoxiclav. Also at day 28, signs of AOM, such as abnormal reflectometry (45% versus 59%; P = 0.017), bulging of the eardrum (10% versus 16%; P = 0.059) and loss of tympanic membrane landmarks (11% versus 22%; P = 0.010) were seen less frequently in azithromycin- than co-amoxiclav-treated children, respectively. Adverse events related to therapy were seen in 11% of azithromycin patients compared with 20% on co-amoxiclav (P = 0.014). CONCLUSIONS: Azithromycin given over 3 days is as effective as co-amoxiclav for treatment of AOM, may result in more complete resolution of tympanic membrane disease, and is better tolerated.