A possible link between allergic rhinitis (AR) and allergic asthma has long been a subject of debate. Surveys report that up to 78% of asthma patients have AR and 38% of patients with AR have asthma. Evidence points to a causal or coincidental relation between these upper and lower airway diseases. Various agents used to manage one entity have shown benefit in treating the other. The 2001 Allergic Rhinitis and Its Impact on Asthma guidelines call for patients with either condition to be assessed for the other. Medical therapy for AR or asthma should be chosen with awareness of the probable coexistence of these diseases. We present the case for and against the united airway theory proposed to explain the association between these diseases. The roles of various therapies for dually afflicted patients are evaluated, including topical corticosteroids, antihistamines, leukotriene modifiers, anti-immunoglobulin E monoclonal antibody, theophylline, and immunotherapy.