The authors describe one case of paraganglioma of the posterior mediastinum successfully removed after being discovered accidentally in a young male patient who showed no symptoms attributable to the tumor. The latter was a round mass, about 6 cm in diameter, richly vascular, located in the right costomediastinal gutter. Histologically it was a functionally silent paraganglioma originating from the intrathoracic aortosympathetic paraganglia, these being part of the very numerous groups of the paragangliar system distributed segmentally into metamers, particularly in the adrenal medulla. According to the more recent views, chemodectoma or paraganglioma (chromaffine or non-chromaffine, functionally active or silent) and pheochromocytoma (functionally active or silent, adrenal or extra-adrenal) constitute a group of tumors sharing the same tissue matrix, namely paragangliar cells.