Acute otitis media and acute bacterial sinusitis are 2 of the most common indications for antimicrobial agents in children. Together, they are responsible for billions of dollars of health care expenditures. The pathogenesis of the 2 conditions is identical. In the majority of children with each condition, a preceding viral upper respiratory tract infection predisposes to the development of the acute bacterial complication. It has been shown that viral upper respiratory tract infection predisposes to the development of acute otitis media in 37% of cases. Currently, precise microbiologic diagnosis of acute otitis media and acute bacterial sinusitis requires performance of tympanocentesis in the former and sinus aspiration in the latter. The identification of a virus from the nasopharynx in either case does not obviate the need for antimicrobial therapy. Furthermore, nasal and nasopharyngeal swabs are not useful in predicting the results of culture of the middle ear or paranasal sinus. However, it is possible that a combination of information regarding nasopharyngeal colonization with bacteria and infection with specific viruses may inform treatment decisions in the future.