Nose and lungs are considered as anatomic and functional unit, as they share morphological, pathophysiological and immunological basis. Allergic rhinitis and asthma often coexist in the same individual, and the treatment of one also improves the symptoms of the other (one airway, one disease). The aim of this review is to discuss the interaction between upper and lower airways, based on recent scientific evidence and, critically, analyze the important implications the new findings have for the future therapy and prevention of these common diseases.