INTRODUCTION: Otitis media and acute otitis media (AOM) are the most common diseases among children in the U.S. with an annual cost of more than $3 billion in 1996. Historically, a ten-day course of antibiotics has been the standard treatment for AOM. Providers can choose first-line antibiotics (Amoxicillin, Trimethoprim-Sulfamethoxazole, and Erythromicin-Sulfisoxazole) or a group of second-line antibiotics. Second-line antibiotics generally have a broader spectrum of activity but are more costly relative to first-line antibiotics. Presently, policy makers have little evidence to evaluate the increased effectiveness of second-line antibiotics for AOM in practice. OBJECTIVES: As a first step to address this question, this study describes the factors related to the choice between first-line and second-line antibiotics for initial AOM in Iowa Medicaid population. METHODS: We identified 19,987 Iowa Medicaid eligible children less than 13 year of age who had initial AOM from 1990 through 1997. We estimated the probability of the second-line agent use across the patient demographics (age, sex), previous antibiotic use, year of diagnosis, patient's county, and the specialty of the treating physician. RESULTS: Factors of age (p<0.01), county (p<0.01), previous antibiotic use (p<0.01), provider specialty (p<0.01), and year of diagnosis (p<0.01) had statistically significant effects on second-line prescribing. We found that second-line prescribing increased over time. With respect to specialty, general practitioners (OR=1.33, 95% CI=1.18-1.49), family practitioners (OR=1.10, 95% CI=1.01-1.19), and otolaryngologists (OR=1.83, 95% CI=1.53-2.18) were more likely to prescribe second-line antibiotics than pediatricians. In addition, the affect of the timing of previous antibiotic use on second-line prescribing varied with type of antibiotic previously used. Any second-line antibiotic used within the last 180 days was positively related to second-line antibiotic use for initial AOM. However, only first-line antibiotic use within the last 60 days contributed to increased second-line use.