Acute bacterial sinusitis (ABS) is an extremely common problem in both children and adults. There are three clinical presentations of acute sinusitis: (1) onset with persistent symptoms (nasal symptoms or cough or both for > 10 but < 30 d without evidence of improvement); (2) onset with severe symptoms (high fever and purulent nasal discharge for 3-4 consecutive days); and (3) onset with worsening symptoms (respiratory symptoms, with or without fever, which worsen after several days of improvement). Images to confirm the presence of acute sinusitis are necessary in older children (> 6 years) and adults to enhance the certainty of diagnosis. The predominant bacterial species that are implicated in acute sinusitis are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in children. In the last decade, there has been an increasing prevalence of penicillin-resistant S. pneumoniae, and beta-lactamase-producing H. influenzae and M. catarrhalis. Although there has been some controversy in the literature regarding the effectiveness of antibiotics in the treatment of ABS, most studies in which the diagnosis of acute bacterial sinusitis is confirmed with images and appropriate anti-biotics are prescribed show superior outcomes in recipients of antibiotics. Therapy may be initiated with high-dose amoxicillin or amoxicillin-clavulanate. In penicillin-allergic patients or those who are unresponsive to amoxicillin, amoxicillin-clavulanate is appropriate. Alternatives include cefuroxime, cefpodoxime, or cefdinir. In cases of serious drug allergy, clarithromycin or azithromycin may be prescribed. The optimal duration of therapy is unknown. Some recommend treatment until the patient becomes free of symptoms and then for an additional 7 d.