Hyalinizing trabecular tumors of the thyroid have been described on 4 occasions, by Carney and colleagues in 1987, by Ward and coworkers in 1982, by Pierre Masson in 1922, and by Rahel Zipkin in 1905. Zipkin credited her chief, Theodor Langhans (of Langhans giant cell fame), with identification of the cases she reported. Unaware of the 3 earlier descriptions, Carney and colleagues described 11 circumscribed or encapsulated thyroid tumors with elongated and polygonal cells arranged in trabeculae that contained a hyaline material resembling amyloid. The nuclei of the tumor cells had cytoplasmic invaginations and grooves similar to those of papillary carcinoma. Carney and colleagues labeled the neoplasms hyalinizing trabecular adenomas because of their microscopic appearance, absence of invasion, and benign natural history. Subsequently, the nuclear features of the tumor and the molecular genetic findings led to the introduction of equivocal designations for it, hyalinizing trabecular tumor and hyalinizing trabecular neoplasm, and later to its designation as a variant of papillary carcinoma. Experience has shown that most circumscribed or encapsulated follicular thyroid tumors with intratrabecular hyalin and nuclear features of papillary carcinoma behave as benign neoplasms. Hyalinizing trabecular carcinoma is a very rare tumor.