Rhinitis and sinusitis are prevalent medical conditions that are often associated with each other and may result in significant morbidity and medical costs. They can cause systemic symptoms, decrease quality of life, and result in reduced workplace productivity and missed school days. Appropriate management of rhinitis or sinusitis may be an important component in effective management of coexisting or complicating conditions, such as asthma, allergic conjunctivitis, or chronic otitis media. Rhinitis may be caused by allergic, non-allergic, infectious, hormonal, occupational, and other factors. Defining the basis for rhinitis in an individual is important in selection of therapeutic options. Rhinitis and sinusitis may be difficult to distinguish from each other on the basis of history alone. Although most acute upper respiratory infections are viral and do not require antibiotic treatment, persistence of symptoms for ≥7 days makes acute bacterial sinusitis more likely and antibiotics an appropriate consideration. Radiographic imaging is not required for diagnosis of acute, uncomplicated sinusitis, although CT scans are indicated in evaluation of suspected chronic sinusitis or treatment failures. Chronic sinusitis may have an infectious or non-infectious basis. Underlying disorders that predispose to chronic sinusitis should be identified and treated as part of the treatment of chronic sinusitis. (J Allergy Clin Immunol 2003;111:S520-9.)