We report here a case in which for hemoptysis during menstruation (catamenial hemoptysis) right middle lobectomy was performed thoracoscopically under a preoperative diagnosis of pulmonary endometriosis with a successful outcome. The patient was a 27-year-old housewife who from the age of 24 years experienced hemoptysis during menstruation, and was diagnosed as having pulmonary endometriosis on the basis of detailed examinations including bronchoscopy and chest CT. From the age of 26 years hormone therapy was administered, but the hemoptysis recurred with the menstruation following its cessation. After admission to this department bronchoscopy performed at the time of menstruation revealed bleeding from right B4 while chest CT showed an abnormal shadow in right S4 b. Right middle lobectomy was then performed thoracoscopically under a diagnosis of right middle lobe endometriosis. In the resected specimen findings of pulmonary hemosiderosis, granulomatous phlebitis and micrometastases from a thyroid cancer were noted. The postoperative course was favorable with no further episodes of hemoptysis occurring. In this case histological proof of endometriosis could not be obtained, but the diagnosis of pulmonary endometriosis was strongly suggested by the clinical course and objective findings such as pulmonary hemosiderosis.