Two medullary carcinomas of the thyroid (MCTs) composed entirely of Hürthle (oncocytic or oxyphilic) cells and containing follicular structures are described. Immunocytochemical analysis showed these tumours to be calcitonin-, carcino-embryonic antigen- and neuron-specific enolase-positive. The essence of this communication is twofold. Firstly, it highlights and draws attention to this unusual variant of MCT, which may be encountered at frozen section and misdiagnosed as a Hürthle cell tumour of follicular cell origin. Secondly, it undertakes a concise overview of the immunocytochemistry of Hürthle cell thyroid neoplasms and MCT.