The X-ray CT findings of two cases of pulmonary lymphangioleiomyomatosis were reported. The correlation between high-resolution CT findings and inflated biopsy specimens was studied. The X-ray CT findings are 1) multiple low attenuation areas, 2) diffuse areas of slightly increased density and 3) irregular enlargement of pulmonary vascular images. Each low attenuation are turned out to correspond to emphysematous lesions. Slightly increased densities on CT images seemed to be caused by a summation of many small nodules of a proliferation of smooth muscle cells located in the wall of respiratory bronchioles and alveolar ducts, with or without intraalveolar hemosiderosis. Some nodular lesions in bronchiolar walls were so close to neighboring vessels that they could not be separated from vascular images on CT, so peripheral vascular images were irregularly thickened. X-ray CT reflected more actual pathological findings than routine chest radiographs. As low attenuation areas on CT images have been reported to be representative of pulmonary emphysema, it is thought that the above CT findings must be differentiated from those of pulmonary emphysema. While pulmonary vascular images were thin and stretched on the CT in patients with emphysema, they were irregularly thickened on the CT of patients with LAM. Furthermore, while CT of emphysema often revealed overinflation or decreased density, diffuse areas of slightly increased density were never found in emphysema.