There have been 17 reported cases of histologically proved thoracic endometriosis and 27 cases of probable thoracic endometriosis based upon repetitive symptoms associated with menstruation and response to suppression of ovarian function. Two additional cases of probable thoracic endometriosis are reported. Seventeen of these 46 patients also had proved pelvic endometriosis and four others had clinical evidence of pelvic disease. In the majority of the cases there has been a delay in diagnosis accompanied by prolonged disability.