Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the etiologic agents of acute bacterial sinusitis (ABS). Staphylococcus aureus has been an uncommon cause of ABS despite its frequent occupancy within the anterior nares. A quantitative culture of a maxillary sinus aspirate is the gold standard for determining etiology of ABS. Cultures of the middle meatus cannot be used as a surrogate for a maxillary sinus aspirate in children with ABS, although they may be used in adults if interpretation is confined to usual sinus pathogens. Recent studies highlighting S. aureus as a major pathogen in ABS should be interpreted cautiously. Most isolates in recent pediatric studies were derived from cultures of the middle meatus. The range of reported results for the incidence of S. aureus as a cause of ABS in adults is similar to the results reported for staphylococcal colonization of the middle meatus in healthy adults.