Acute rhinosinusitis causes more than 30 million patients to seek health care per year in the United States. Respiratory tract infections, including bronchitis and sinusitis, account for 75% of outpatient antibiotic prescriptions in primary care. Sinusitis is a clinical diagnosis; the challenge lies in distinguishing between the symptoms of bacterial and viral sinusitis. Cardinal features of acute bacterial rhinosinusitis are unilateral facial pain or pressure, fever greater than 102°F (39°C), and purulent nasal discharge with obstruction of the nasal passages. Antibiotics should be considered for patients with 3 or more days of severe symptoms, significant worsening after 3 to 5 days of symptoms, or 7 or more days of symptoms. Diagnostic testing for acute rhinosinusitis with antral puncture is impractical because of its invasiveness. Point-of-care testing for elevated C-reactive protein may be helpful, but it is not widely available. Studies have shown that amoxicillin is as effective as amoxicillin-clavulanate as a first-line treatment for acute bacterial rhinosinusitis for those without a beta-lactam allergy. For patients with a beta-lactam allergy, appropriate antibiotics include doxycycline or a respiratory fluoroquinolone; clindamycin plus a third-generation cephalosporin is an option for children with non-type I hypersensitivity to beta-lactam antibiotics. Supportive care for rhinosinusitis, including use of saline irrigation, nasal steroids or antihistamines, and decongestants, may help reduce the severity of symptoms. Most episodes of rhinosinusitis are self-limited, lasting 7 to 10 days. Complications of rhinosinusitis are rare but may include orbital cellulitis, meningitis, and abscess. Computed tomography and referral to an otolaryngologist should be considered for patients with recurrent rhinosinusitis or concern about complications.