Hyalinizing trabecular tumors of the thyroid are interesting but uncommon neoplasms. They have been classified as benign hyalinizing trabecular adenomas or malignant hyalinizing trabecular carcinomas. They share both epidemiologic and morphologic features with papillary carcinoma, and there has been much speculation about the relationship between these two entities. Because RET/PTC gene rearrangements are specific to papillary thyroid carcinoma, the authors examined the presence of RET/PTC-1, -2, and -3 in eight hyalinizing trabecular tumors using reverse transcription-polymerase chain reaction with Southern hybridization and immunohistochemistry. They detected the presence of a RET/PTC gene rearrangement in six of the eight hyalinizing trabecular tumors. This confirms the long-standing suspicion that hyalinizing trabecular tumors do indeed represent a morphologic variant of papillary carcinoma.