Clinical, roentgenographic and pathologic findings are described in 9 patients with fungal tracheobronchitis and comparison is made with 25 additional cases in the literature. Two morphologic patterns were identified: the first appears as a pseudomembrane of necrotic tissue, exudate, and fungal hyphae involving more-or-less the entire circumference of the bronchial wall or as mucus/fungus plugs completely occluding the airway lumen; the second consists of single or multiple discrete plaques on the airway wall, sometimes associated with invasion of the adjacent lung parenchyma or pulmonary artery. As with more invasive forms of fungal infection, a compromise in host defenses is probably the most important factor leading to fungal colonization and subsequent local invasion. Malignancies of the hematologic and lymphoreticular systems, solid neoplasms, granulocytopenia, and a history of a protracted course of broad-spectrum antibiotics, corticosteroids, and chemotherapy were present in most of our patients and in those reported in the literature. Despite this, there is some evidence that tracheobronchitis may occur in individuals with a relatively lesser degree of host defense impairment. Local damage to the airway wall such as occurs with prolonged mechanical ventilatory support, neoplastic infiltration, or nonfungal infection may also be a factor predisposing to fungal colonization and invasion. In 4 of our patients, the fungal infection of the tracheobronchial tree probably contributed significantly to the development of terminal respiratory failure. Although recognition of the infection may not have altered the course of the underlying disease in some of our patients, in others identification and early treatment might have been life-saving. Thus, culture and histologic examination of bronchoscopically identified tracheobronchial mucus plugs and necrotic material should be performed in all immunocompromised individuals.