Bacteriology of the ethmoid bullae in children with chronic sinusitis. Cultures from 105 children with chronic sinusitis who had failed aggressive medical management were retrospectively studied. Patients with immunodeficiency and cystic fibrosis were excluded from the study. Because the most common sites of disease were the infundibula and anterior ethmoid sinuses, samples of mucosa removed from the anterior ethmoid bullae during endoscopic ethmoidectomy were routinely cultured for aerobic and anaerobic organisms. Fungal cultures were performed for 55 bullae. The principal organisms isolated were alpha-hemolytic Streptococcus, Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pneumoniae, and Haemophilus influenzae non-type B. Only 12 anaerobic organisms and four fungi were isolated. Of the 204 bullae cultured, multiple organisms were found in 61 bullae and 40 showed no growth. Isolates of other less common organisms were also found. These data are analyzed on the basis of age and duration of symptoms, and antibiotic treatment is described. 