Otitis media (OM) is a common childhood disease and one which can cause significant morbidity. A knowledge of the pathogens responsible for OM enables the most appropriate treatment regimen to be selected and thus minimizes further complications which may require hospital admission and surgery. The microbiology of acute, serous and chronic OM is reviewed, with particular regard to the role of anaerobic bacteria. Anaerobes, mainly Gram-positive cocci, have been recovered from 25% of the ear aspirates of patients with acute otitis media. In a study of serous OM, anaerobic bacteria were recovered in 12% of the culture-positive aspirates. The predominant anaerobes were Gram-positive cocci and pigmented Prevotella. Several studies have reported the recovery of anaerobes from about 50% of patients with chronic OM and those with cholesteatoma. The predominant anaerobes were Gram-positive cocci, pigmented Prevotella, Porphyromonas sp., Bacteroides spp. and Fusobacterium spp. Many of these organisms produce beta-lactamase which might have contributed to the failure of the patients to respond to penicillins. The appropriate antimicrobial therapy for acute, serous and chronic otitis media is discussed.