Patients with acute sinusitis often have purulent nasal discharge, facial pain, and congestion, whereas those with chronic sinusitis have more subtle signs. Infection, hyperreactivity reactions, anatomic obstruction, and underlying disease are among the causes and must be differentiated before appropriate care can be offered. Plain films and sinus transillumination may provide clues in adults but are of little value in young children. Computed tomography is much more sensitive but should be reserved for patients in whom maximal medical therapy has failed, who have a confusing presentation, or who are being considered for endoscopic surgery. Antibiotic therapy is still effective for bacterial infections, but penicillin-resistant organisms are on the increase. If there is no clinical improvement in 3 days, an agent with a broader spectrum of activity should be considered. A combination of agents and prolonged administration may be required for chronic sinusitis, and patients with recurrent symptoms may need endoscopic surgery. Such adjunctive agents as decongestants and saline or steroid nasal sprays may promote drainage. Antihistamines have no role in the treatment of sinusitis.