Molecular markers of papillary thyroid carcinoma (PTC) are relatively unknown. Recently, the CITED1 gene was reported to be greatly upregulated in PTC relative to normal thyroid. The CITED1 protein, a 27-kd transcriptional transactivator nuclear protein is expressed in PTC, melanocytes, breast epithelial cells, and several embryonic tissues. However, its expression in other thyroid masses and non-thyroid tumors is not known. We evaluated CITED1 protein expression in tissue microarrays comprising various thyroid and nonthyroid tissues by immunohistochemistry using a polyclonal anti-CITED1 antibody. CITED1 expression was seen in 63 of 68 PTC (93%), 3 of 12 follicular carcinomas (25%), 2 of 7 Hürthle cell carcinomas (28%), 2 of 21 adenomas (10%), 2 of 6 follicular neoplasms of undetermined malignant behavior (33%), and 2 of 24 nodular goiters (8%). Normal thyroids (n = 27), thyrotoxic hyperplasias (n = 14), and anaplastic thyroid carcinomas (n = 5) did not express CITED1. Among nonthyroid tumors, 6 of 23 melanomas (26%), 11 of 65 prostatic carcinomas (17%), 3 of 25 glioblastomas (12%), 4 of 67 breast carcinomas (6%), 1 of 49 lymphomas (2%), 1 of 65 lung carcinomas (2%), 1 of 68 colon carcinomas (2%), and none of 49 ovarian carcinomas (0%) expressed CITED1. The accuracy of CITED1 in differentiating PTC from benign thyroid nodules, other thyroid carcinomas, and nonthyroid carcinomas was 93%, 89%, and 94%, respectively. CITED1 is preferentially expressed in PTC and may be used as a diagnostic marker of it.