The oncocyte is a peculiar cell found in the aging parotid gland. A precise definition of oncocytic tumors in now available using histochemical and electron microscopic techinques. Oncocytic carcinomas are very rare; only a handful have been cited in the literature. This is the first description of the electron microscope features of oncocytic carcinomas we can find in the literature. The cells of these carcinomas are characterized by mitochondrial hyperplasia, pleomorphism and atypism. The cells contained few other subcellular organelles and no myofilaments or glycogen as previously described in benign oncocytomas. In addition to these electron microscopic features, the clinical presentation, treatment, and biologic course of these three cases of oncocytic carcinoma and two cases of benign oncocytoma will be presented.