In 1982, a 45-year-old woman was hospitalized because of an abnormal lung shadow. The chest film provided evidence of pulmonary nodules. She was asymptomatic and had no labolatory abnormalities. Exploratory excision was performed to further assess the pulmonary nodules. The initial diagnosis was a suspected "hemangiopericytoma". She received combination chemotherapy but it was not effective. The nodules increased and decreased in size and number over the next decade from 1982, reaching a maximum by 1990 and a minimum by the end of 1992. However, her clinical condition remained stable during this period. Retrospective immunohistochemical analysis of CD10 and progesterone receptors confirmed a diagnosis of pulmonary parenchymal endometriosis. This was an unusual case of pulmonary parenchymal endometriosis that demonstrated various changes in the size and number of nodules without symptoms. There are few previous reports that demonstrated such nodular variation without symptoms over the course of disease.