Lymphangioleiomyomatosis (LAM) is regarded as a form of interstitial lung disease but is actually a low grade neoplasm now thought to originate in the uterus. LAM may be sporadic but is also strongly associated with tuberous sclerosis. LAM cells carry mutations in the TSC2 or TSC1 gene, a defect that allows unconstrained activity of the mTORC1 complex leading to cell proliferation and invasiveness. Estrogen is an additional driver of LAM cell proliferation and metalloprotease production. In the lung, LAM appears as cysts with a variable lining of smooth muscle-like LAM cells. Multifocal micronodular pneumocyte hyperplasia may also be present. Outside the lung, LAM is associated with renal angiomyolipomas and lymphangiomas in various organs. Treatment of LAM patients with an mTOR inhibitor (Sirolimus or Everolimus) halts progression of the disease and causes variable degrees of shrinkage of LAM lesions.