The sonographic textures of 10 parathyroid tumors in nine patients were examined and compared with their histologic features, particularly with the amount of fibrous trabeculae. The carcinomas containing a large amount of fibrous trabeculae, which is the most frequent finding in parathyroid cancer, were very echogenic. On the other hand, the adenomas without fibrous trabeculae showed a low echogenicity. These data suggest that the possibility of malignancy is high when the parathyroid tumor is found to be very echogenic. Indexing Words: Parathyroid gland -Ultrasonography -Neoplasm Computed tomography and selective thyroid venous sampling combined with parathyroid hormone assays have made it easier to detect the correct location of parathyroid tumors. 'y2 However, information relating to the histologic features of each tumor cannot be obtained by these methods. Most parathyroid cancers have been reported to have coarse fibrous trabeculae histologially.^,^ It might therefore be expected that the acoustic impedances of the fibrous trabeculae and the cells in parathyroid tumors would be different, and thus echoes would be generated at the interface formed by these two different tissues. If so, the tumor with fibrous trabeculae should exhibit significant echogenicity . To confirm the validity of our assumption, we investigated the sonographic textures of various parathyroid tumors in nine patients and compared them with From the *Third