An example of lymphoepithelial carcinoma of the thyroid is reported, which was first described 10 years ago and has not as yet been documented in the German literature. This tumour is morphologically identical to the lymphoepithelioma of the nasopharynx. In contrast to neoplasms of such morphology occurring in a variety of other organs, the acronym CASTLE--for carcinoma showing thymus-like differentiation--has been proposed by Chan and Rosai for lymphoepithelioma-like carcinomas of the thyroid gland. In this paper, the aforenamed authors' concept of the histogenesis of thyroid tumours with thymic differentiation is presented.