We sought to correlate the clinical, radiographic, and bacteriologic findings in maxillary sinusitis in 30 children who had both upper-respiratory-tract symptoms and abnormal maxillary radiographs. Cough, nasal discharge, and fetid breath were the most common signs, but fever was present inconsistently. Facial pain or swelling and headache were prominent symptoms in older children. Bacterial colony counts of greater than or equal to 10(4) colony-forming units per milliliter were found in 34 of 47 sinus aspirates obtained from 23 children. The most common species recovered were Streptococcus pneumoniae, Haemophilus influenzae, and Branhamella catarrhalis. No anaerobic bacteria were isolated. Viruses were isolated from only two sinus aspirates. There was a poor correlation between the predominant species of bacteria recovered from either the nasopharyngeal or throat culture and the bacteria isolated from the sinus aspirate. This study demonstrates that children with both upper-respiratory-tract symptoms and abnormal sinus radiographs are likely to harbor bacteria in their sinuses, suggesting that such children have bacterial sinusitis.