• Seventeen cases of subperiosteal inflammation of the orbit secondary to sinusitis were analyzed from a bacteriological perspective. The recovered pathogens ranged from single aerobes to mixed aerobes and anaerobes. The bacteriology was not related to the duration of symptoms of sinusitis. Three cases with the diagnostic criteria for subperiosteal inflammation resolved with antibiotics alone. The most refractory infections had the most complex bacterial constituencies and persisted despite in vitro antibiotic susceptibility of individual organisms. In these cases, local physical conditions may be drastically altered in favor of the bacteria. Ventilation of the subperiosteal space and sinuses by surgical drainage can help to normalize the milieu in favor of the host.