Lymphangioleiomyomatosis is characterized by cystic destruction of the lungs due to abnormal proliferation of smooth muscle cells. It is caused by mutations of the genes encoding hamartin and tuberin, sometimes in association with tuberous sclerosis. CT imaging shows characteristic multiple thin-walled cysts. There is usually progressive airways obstruction and impaired gas diffusion, and two-thirds of patients suffer pneumothoraces. Sirolimus can stabilize lung function and improve symptoms. Patients should avoid exogenous oestrogens, including oestrogen contraceptives or hormonal replacement therapy. Pregnancy may be associated with an increased risk of pneumothorax and loss of lung function. Hormonal therapy with progesterone or tamoxifen appears to be ineffective: other antioestrogen therapies, such as letrozole, are being studied. Lung transplantation is the main option for advanced disease.