Fibrosing alveolitis, or interstitial pulmonary fibrosis, is a common manifestation of neurofibromatosis, and was observed in 7 of 70 patients with the disease. Though neurofibromatosis is congenital, fibrosing alveolitis does not appear until adulthood, and occurs in 20% of patients with the disease who are over 30 years old. Characteristic radiographic findings include linear, interstitial density, and large upper lobe bullae; this combination limits the differential diagnosis. Pathological examination demonstrates alveolar wall thickening progressing to fibrosis and lung destruction. Pulmonary function tests can show obstructive or restrictive lung disease.