Over 700 cases of anaerobic osteomyelitis have been reported in the literature. Nonetheless, most reviews of osteomyelitis have paid little attention to the potential role of anaerobes in bone infections. There have, as yet, been no prospective studies of osteomyelitis utlizing optimal anaerobic transport and culture techniques. In a retrospective study of osteomyelitis at Wadsworth VA Hospital from 1973--1975, 39 percent of 58 patients with osteomyelitis had an infection involving anaerobes. Anaerobes were isolated from 81 percent of 27 patients whose specimens were cultured anaerobically. Anaerobes were isolated from nine of ten samples of bone. Anaerobic bacteria were part of a mixed flora involving facultative bacteria in all but two cases. All of the patients with anaerobic infection had non-hematogenous osteomyelitis. Non-hematogenous disease comprises 80--90 percent of the osteomyelitis seen in adults. Our experience at Wadsworth VA Hospital and a review of the literature lead us to believe that anaerobes play a much larger role in osteomyelitis than has been appreciated previously. Infections of the calvarium, mastoid, mandible, maxilla and the extremities are most likely to involve anaerobes. Predisposing conditions include paranasal sinusitis, otitis media, periodontal disease, trauma, peripheral vascular disease, peripheral neuropathy and/or chronic osteomyelitis. The presence of a foul odor is a valuable clinical clue to the presence of anaerobes. Bacteroides, fusobacteria and anaerobic cocci have been reported with almost equal frequency from anaerobic bone infections. While Bacteroides fragilis is the most common anaerobe isolated in infections of other organ systems, it does not appear to be a common pathogen in anaerobic bone infections. The role of anaerobes in osteomyelitis is not yet resolved. They have been isolated in pure culture from infected bone, and under those circumstances are clearly pathogenic. Anaerobes are found more frequently as part of a mixed flora with facultative streptococci, gram-negative bacilli, and less often with S. aureus. In this setting it is unclear which organism or organisms are the primary invaders, or whether there is a synergistic mechanism of infection. The reliability of sinus drainage cultures also remains to be determined. Our retrospective study suggests that certain anaerobes isolated from sinus drainage are not present in infected bone. Cultures of bone or an abscess adjacent to bone would be expected to give more reliable data. The majority of anaerobes other than B. fragilis are susceptible to levels of penicillin achievable with parenteral administration of the antibiotic. Anaerobic pathogens should be sought in the situations noted above. We feel that parenteral penicillin should be part of the initial antibiotic regimen in patients with suspected or documented anaerobic bone infection...