Substantial evidence exists to support the concept that the respiratory system functions as an integrated unit. Pathophysiological processes that involve the upper airway generally occur in conjunction with lower airway diseases, and diffuse inflammation often affects mucosal surfaces of the middle ear, nose, sinuses, and tracheobronchial tree simultaneously. Support for this relationship can be found in epidemiological studies, in shared pathophysiological mechanisms, and in observed interactive treatment effects. This model and its implications are discussed.