- Objectives: To determine clinical characteristics of AOM at presentation and during therapy according to specific etiologies. Patients and Methods: 1003 patients studied during 1996–2001 in antibiotic efficacy studies underwent tympanocentesis and middle ear fluid culture at enrollment and on Day 4–6 (in initially culture-positive patients only). We used a clinical/otologic (CO) score for evaluating severity of fever, irritability and tympanic membrane redness and bulging (0–3 each parameter, maximal score = 12). Results: Seven hundred sixty-three patients had positive cultures with 392 (39%) Haemophilus influenzae, 198 (20%) Streptococcus pneumoniae and 173 (17%) mixed H. influenzae and S. pneumoniae infection. Mean CO score was higher in culture-positive versus culture-negative patients (8.21 ± 2.17 vs. 7.73 ± 2.32, p = 0.003) regardless of isolated organism. A marked improvement in CO score was observed on Day 4–6 in all patients: 1.83 ± 2.18 in children initially culture-positive and 0.9 ± 1.67 in those initially culture-negative (p < 0.001). The improvement was greater in patients with eradication versus those with bacteriological failure (CO score 1.52 ± 1.82 vs. 2.77 ± 2.85, p < 0.001). Conclusions: CO score before treatment, after bacterial eradication or in bacteriologic failures are similar in bacterial AOM and are not predictive of the etiology of the disease.