Fibrosing alveolitis, a condition characterized by a poor prognosis and a limited response to treatment, is readily identified by thin-section computed tomography (CT). Fibrotic and inflammatory histologic results, obtained at open lung biopsy, both have characteristic CT patterns. To evaluate whether CT could predict prognosis and response to therapy, we examined the CT appearances of 76 patients with lone cryptogenic fibrosing alveolitis and 66 patients with fibrosing alveolitis associated with systemic sclerosis. CT abnormalities were categorized as predominantly a ground-glass pattern (Grade 1), mixed (Grade 2), or predominantly a reticular pattern (Grade 3). In cryptogenic fibrosing alveolitis, 4-yr survival was highest in association with CT Grade 1 and higher with CT Grade 2 than with CT Grade 3, independent of the extent of abnormal lung on CT, duration of dyspnea, or severity of depression of DLCO or FVC, p < 0.001. A response to therapy in previously untreated cryptogenic fibrosing alveolitis was seen most frequently with CT Grade 1 and more frequently with CT Grade 2 than with CT Grade 3, p < 0.025. In systemic sclerosis, CT appearances were not predictive of 4-yr survival; a response to therapy was seen more frequently with CT Grade 2 (three of seven patients) than with CT Grade 3 (zero of six patients). These data have shown that CT appearances are of prognostic value in fibrosing alveolitis and that they are likely to play an increasing role in disease-staging in this condition.