A 38-year-old female was admitted due to progressive exertional dyspnea and intermittent blood tinged sputum. Chest PA showed diffuse reticular infiltration accompanied by hyperinflation. $PaO_2$ was normal in resting state but profoundly decreased during exercise. Spirometry showed severe obstructive pattern but DLCO was markedly decreased. Lung volumes measured by helium equilibrium method was increased. On HRCT, numerous and relatively uniform sized cysts were evenly distributed throughout the bilateral lung fields. Open lung biopsy was performed and pulmonary lymphangioleiomyomatosis(LAM) was diagnosed based on the findings of abnormal proliferation of smooth muscle cells in the walls of lymphatic vessels, bronchioles, and small pulmonary veins. Immunohistochemical staining was negative for estrogen receptor but positive for progesterone receptor. Medroxyprogesterone therapy was initiated.