Chest radiographs, thin-section computed tomographic (CT) scans, and results of pulmonary function tests in nine women with pulmonary lymphangiomyomatosis and two women with pulmonary tuberous sclerosis were retrospectively evaluated. In all patients, CT demonstrated thin-walled cysts less than 20 mm in diameter scattered at random in all parts of the lungs. In eight patients, cysts larger than 20 mm in diameter were also present. Lung tissue between cysts appeared normal in all 11 patients, except one with septal lines and dependent alveolar areas of attenuation. CT showed cysts in three patients whose radiographs were normal, and it demonstrated that many lesions that appeared reticular on plain radiographs were actually cysts. CT findings correlated better with the diffusion capacity of the lungs for carbon monoxide than did the plain radiographic findings. CT was more sensitive and more precise than radiography at showing the presence and morphology of lung abnormalities.