The upper airway is generally defined as the air passage segment that extends between the naso- or oropharynx and the carina. The longest segment of the upper airway-the trachea-begins at the inferior portion of the larynx and extends to the branch point of the main carina. The trachea has the potential to be a "forgotten zone" in differential diagnoses, as pathological processes involving this portion may not receive prominent clinical consideration in disorders presenting with respiratory symptoms and signs. Unlike the oropharynx, this anatomical area is beyond visualization on routine inspection; unlike the mediastinum and lung fields, it is a potential "blind spot" on initial, plain radiographic examination of the chest. Nonetheless, the adult trachea is affected by a number of primary disorders and is also a target organ of a variety of systemic diseases. This review will focus on both primary and systemic diseases involving the adult trachea with specific attention to their clinical manifestations and diagnostic hallmarks.