To better understand the factors involved in chronic sinusitis in childhood, we cultured the sinuses, middle meatus, and nasopharynx in 39 children requiring surgical intervention. Sixty-nine percent of these patients had other medical problems, including asthma (49%) and immunologic compromise (18%). We cultured coagulase-negative staphylococcus in 18 patients, Streptococcus viridans in 14 patients, normal flora in 10 patients, Staphylococcus aureus in nine patients, group D streptococcus in five patients, Corynebacterium in five patients, Haemophilus influenzae in three patients, Neisseria in three patients, and Streptococcus pneumoniae, group A streptococcus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca, Propionibacterium acnes, Actinomyces, and an anaerobic gram-negative bacillus in one patient each. Cultures yielded no growth in nine patients. A strong association between cultures of the middle meatus obtained ipsilaterally and cultures of the maxillary (83%) and ethmoid sinuses (80%) occurred. A poor correlation was found between cultures of the nasopharynx and maxillary (45%) and ethmoid sinuses (49%). All seven patients who had both maxillary and ethmoid sinus cultures showed the same organisms in both sinuses. Only 41% of organisms were found on both sides when procedures were performed bilaterally. Cultures of the middle meatus appear to be sensitive and specific for organisms within sinuses. The presence of predominantly nonvirulent organisms in low titers suggests that additional factors other than bacterial overgrowth contribute to the pathogenesis of chronic sinusitis in children.