PURPOSE: To present initial and follow-up HRCT findings of lymphangitic carcinomatosis of the lung. MATERIALS AND METHODS: Both initial and follow-up HRCT scans were obtained in 18 patients with lymphangitic carcinomatosis of the lung. After dividing the patients into two groups (with anticancer chemotherapy (n=12) and without chemotherapy (n=6), changes of pulmonary parenchymal abnormalities (percentile increase or decrease in the extent of each pattern) were assessed and compared on initial and follow-up HRCTs. RESULTS: Findings on initial CT were interlobular septal thickening (n=18) (smooth in 15 and mixed smooth and nodular in three), thickening of bronchovascular bundles (n=17), areas of ground-glass opacity (n=15), polygonal lines (n=15), and nodules (n=10). With chemotherapy, the finding of polygonal lines decreased by 20/3%, while findings of ground-glass opacity, bronchovascular bundle thickening, septal thickening, and nodules remained stable. Without chemotherapy, all CT patterns of abnormalities except nodules increased by 45-88%. In three patients who did not undergo chemotherapy, smooth interlobular septal thickening changed to nodular thickening. CONCLUSION: Lymphangitic carcinomatosis of the lung manifests initially as smooth thickening of the interlobular septae, bronchovascular bundle thickening,areas of ground-glass opacity, and polygonal lines, as seen on HRCT. Without chemotherapy, the extent of CT findings increases and there is a tendency for smooth septal thickening to change to nodular thickening. Chemotherapy induces improvement or cessation of the progression of CT findings.