To improve the diagnosis and treatment of patients with acute bacterial sinusitis and reduce the inappropriate use of antibiotics, clinical guidelines have been developed by three national organizations: the American Academy of Pediatrics, the Sinus and Allergy Health Partnership and the Centers for Disease Control and Prevention. Traditionally, the diagnosis of acute bacterial sinusitis is suspected on the basis of clinical signs and symptoms and is confirmed with the performance of images (either plain radiographs, computed tomography or magnetic resonance imaging). All three guidelines recommend that the diagnosis and treatment of acute bacterial sinusitis should be based on clinical criteria alone without the confirmation of imaging or other laboratory data. Although the similarity between the different guidelines suggests that there is widespread consensus to use clinical criteria to diagnose acute bacterial sinusitis, there is virtually no evidence to support this position. Specific Aim 1 of this project is to evaluate the use of clinical criteria, without the performance of images, as the basis for the diagnosis of acute bacterial sinusitis. A randomized, placebo-controlled study design will be used to determine if the clinical criteria proposed by the different guidelines can be used to identify children with upper respiratory symptoms who will respond to antibiotic therapy. It is expected that children with acute bacterial sinusitis who receive an antimicrobial will recover more quickly and more often than children who receive placebo.