Background: The need for antimicrobials in the treatment of subacute sinusitis was evaluated in 96 afebrile children who were prescribed antimicrobial (amoxiicillin, amoxicillin clavulanate pottassium, or trimethoprim-sulfamethoxazole) or no antimicrobial medication in addition to a decongestant and saline nasal spray for 3 weeks. Methods: Response was determined by complete clearing of the initial radiologic abnormalities or in the case of mucosal thickening by a significant decrease in thickness to <6 mm within the maxillary sinuses associated with improvement of the clinical signs and symptoms of sinusitis. If there was evidence of partial clearing by radiograph, the same therapy was continued for another 3 weeks. Nonresponders demonstrated no change or worsening of clinical and radiologic findings. Results: Sixty-seven of the 96 subjects (70%) responded: 58 (87%) in 3 weeks and 9 (13%) in 6 weeks. Fifty-five of the responders were in the antimicrobial treatment group, and 12 were prescribed no antimicrobial medication. Twenty-nine of the 96 subjects (30%) did not respond to treatment; 22 received an antimicrobial and seven received no antimicrobial medication. Conclusions: The number of responders and nonresponders was similar in the antimicrobial- and nonantimicrobial-treated groups (p = NS), and no single antimicrobial medication demonstrated greater treatment effectiveness. © 1993.