Lymphangioleiomyomatosis is a rare disease of unknown cause that affects women of reproductive age. It is characterized by progressive proliferation of smooth muscle in the lung. The patients present with progressive shortness of breath, pneumothorax, chylous effusion, and hemoptysis. Four patients with biopsy-proved lymphangioleiomyomatosis of the lung were evaluated using high-resolution CT. In all patients, the scan showed well-defined cystic air spaces, surrounded by uniformly thin walls, distributed diffusely throughout both lungs. The cystic air spaces ranged in size from a few millimeters to 5 cm. Pathologically, these cysts were predominantly bounded by normal-looking parenchymal components, with occasional patchy involvement by a smooth-muscle proliferative process. The CT appearance of lymphangioleiomyomatosis differs quite distinctly from that of other diseases that can cause cystic air spaces, such as fibrosing alveolitis, neurofibromatosis, and bronchiectasis, and less distinctly from pulmonary emphysema and eosinophilic granuloma. Our experience in these few cases suggests that the high-resolution CT findings in lymphangioleiomyomatosis are characteristic of the disease.