EPIDEMIOLOGY OF THE BACTERIA RESPONSIBLE: Acute otitis media (AOM) is the most common bacterial infection in childhood below the age of 5 years. Bacteria may be isolated from middle ear fluid in about two-thirds of patients. The prevalence of bacteria varies from one country to the next. The most common pathogens recovered are Streptococcus pneumoniae, Haemophilus influenzae (20-50%) and less frequently Moraxella catarrhalis (10%). However, several recent reports suggest an increasing rate of isolation of M. catarrhalis approaching 20%. Concomitant isolation of two or more organisms occurs in up to 10% of cases. The role of Group A Streptococci and Staphylococcus aureus in AOM has decreased since the use of antibiotics. EPIDEMIOLOGY OF ANTIMICROBIAL RESISTANCE: The recent spread of penicillin resistant S. pneumoniae and amoxycillin resistant H. influenzae varies considerably from one country to an other and appears related to the use of antibiotics and socio-economic conditions. A follow up of bacterial epidemiology and antibiotic resistance is necessary in each region of the world to define accurate strategies of acute otitis antibiotherapy.