Acute rhinosinusitis is one of the most common conditions that physicians treat in ambulatory care. Most cases of acute rhinosinusitis are caused by viral upper respiratory infections. A meta-analysis based on individual patient data found that common clinical signs and symptoms were not effective for identifying patients with rhinosinusitis who would benefit from antibiotics. C-reactive protein and erythrocyte sedimentation rate are somewhat useful tests for confirming acute bacterial maxillary sinusitis. Four signs and symptoms that significantly increase the likelihood of a bacterial cause when present are double sickening, purulent rhinorrhea, erythrocyte sedimentation rate greater than 10 mm per hour, and purulent secretion in the nasal cavity. Although cutoffs vary depending on the guideline, antibiotic therapy should be considered when rhinosinusitis symptoms fail to improve within seven to 10 days or if they worsen at any time. First-line antibiotics include amoxicillin with or without clavulanate. Current guidelines support watchful waiting within the first seven to 10 days after upper respiratory symptoms first appear. Evidence on the use of analgesics, intranasal corticosteroids, and saline nasal irrigation for the treatment of acute rhinosinusitis is poor. Nonetheless, these therapies may be used to treat symptoms within the first 10 days of upper respiratory infection. Radiography is not recommended in the evaluation of uncomplicated acute rhinosinusitis. For patients who do not respond to treatment, computed tomography of the sinuses without contrast media is helpful to evaluate for possible complications or anatomic abnormalities. Referral to an otolaryngologist is indicated when symptoms persist after maximal medical therapy and if any rare complications are suspected.