High-resolution CT images were assessed in 39 patients with confirmed interstitial lung disease. 22 patients with fibrosing alveolitis, 12 patients with lymphangitic spread of tumour and 5 patients with lymphangioleiomyomatosis of the lung were included. In fibrosing alveolitis the dominant features on HR-CT were honeycomb cysts with concomitant fibrosis in a predominantly peripheral subpleural distribution. In contrast to this the patients with LAM showed cystic lesions without any predominance--throughout the lung fields and without any fibrotic changes. In lymphangitic spread of tumour, polygonal lines and septal lines as well as nodules were found along the bronchovascular bundles. The patterns seen on HR-CT of the thorax correlate extremely well with the underlying pathology and make it possible to differentiate between the three disease entities by means of characteristic features.