Purpose To investigate the clinicopathologic features and differential diagnosis of oncocytic variant of medullary thyroid carcinoma( MTC). Methods Morphological,immunohistochemical findings on 3 oncocytic variant of MTC cases and electron microscopic findings on 2 of these 3 cases were studied,with review of the relevant literatures. Results The cytoplasm was abundant,eosinophilic and granular with defined margins. The nuclei were enlarged,round to oval. Prominent nucleoli were identified in some cells. Tu...