A case of a benign, cystic intrapulmonary teratoma occurring in the left lobe of a 63-yr-old female is described and the typical clinical symptoms and distinguishing X-ray appearances which may be helpful in diagnosing this rare tumour are mentioned. The connection between the tumor and the segmental bronchus clearly established the true intrapulmonary nature of the lesion in this case and the unusual finding of thymic tissue within the wall supports previous speculation regarding the possible thymic origin of these neoplasms.