We evaluated the CT findings of 21 cases of chroinc diffuse lung disease which were diagnosed with open lung biopsy(7), transbronchial lung biopsy(3), bronchoalveolar lavage(4), occupational history(2), skin biopsy(2), liver biopsy(1), bone marrow aspiration(1), clinical functional and radiographic findings(6). CT scans were obtained by using 8mm collimation at 8mm intervals in all patient, and additional high resolution CT scans(1mm collimation) were also obtained in 17 patients of them. Although the traditional classification method of disease distribution into upper, middle and lower zones was somewhat useful, the model of disease distribution proposed by Bergin and Muller was more useful in evaluation of chroinc diffuse lung diseases. The diseases that were mainly distributed in axial compartment were lymphangitic carcinomatosis(5), sarcoitosis(2) and those in middle compartment were silicosis(2), extrinsic allergic alveolitis(1), hypereosinophilic syndrome(1), unclassifie one(1) and in peripheral compartment were fibrosing alveolitis (idiopathic pulmonary fibrosis(3), Rheumatoid lung(1), scleroderma(1), dermatomyositis(1) And in diffuse panbronchiolitis(3), even distribution of lesions to both axial and peripheral compartments was noted. But in fibrosing alveolitis, some degree of distribution was noted in peripheral compartment and in lymphangitic carcinomatosis and silicosis, some degree of distribution was noted in peripheral compartment. Nodular thickening of bronchovascular bundles was characteristically seen in all cases of lymphangitic carcinomatosis and sarcoidosis. The nodules were 1-5mm in diameter and were composes of tumor cells9in lymphangitic carcinomatosis) and of sarcoid granuloma within lymphatics in the bronchovascular sheath. however patients with sarcoidosis did not have irregular thickened interlobular septa and polygojal line. Dilatation of peripheral airways without dilatation of proximal bronchi was only seen in diffuse panbro chiolitis. Although we experienced only two cases of silicosis, the nodules of silicosis were separated from the pleura at a constant distance and seldom touched to the pleura.