OBJECTIVE: The goal was to determine the clinical effectiveness of prolonged outpatient treatment with trimethoprim/sulfamethoxazole for children with chronic active otitis media. METHODS: We performed a randomized, placebo-controlled trial with 101 children (1-12 years of age) with chronic active otitis media (defined as otorrhea for > or =12 weeks). In addition to a short course of steroid and antibiotic eardrops, children were assigned randomly to receive 6 to 12 weeks of orally administered trimethoprim/sulfamethoxazole (18 mg/kg, 2 times per day) or placebo and were monitored for 1 year. RESULTS: At 6 weeks, 28% of children in the trimethoprim/sulfamethoxazole group and 53% of children in the placebo group had otomicroscopic signs of otorrhea. At 12 weeks, these values were 32% and 47%, respectively. At 1 year, the numbers of children with otorrhea were similar in the 2 groups (25% and 20%, respectively). One child in the trimethoprim/sulfamethoxazole group developed a skin rash. Vomiting or diarrhea was reported for 9% of the trimethoprim/sulfamethoxazole group and 2% of the placebo group. Pure-tone hearing levels and health-related quality of life improved during the study but did not differ between the trimethoprim/sulfamethoxazole group and the placebo group. Pseudomonas aeruginosa was the most frequently isolated bacteria in the otorrhea samples from both groups. CONCLUSIONS: A 6- to 12-week course of high-dose, orally administered trimethoprim/sulfamethoxazole therapy is beneficial for children with chronic active otitis media. The treatment effect is most pronounced with the shorter course and disappears if administration of the medication is discontinued