Neural cell adhesion molecule (NCAM) is an integral membrane glycoprotein that participates in cell-cell interactions. We examined the expression of neural cell adhesion molecule (NCAM) by immunohistochemistry in 65 cases of thyroid disease. In the majority of thyroid tumors, NCAM expression was detected in tumor cells. In chronic thyroiditis, Hurthle cells demonstrated expression of NCAM. In normal thyroid gland, neither follicular nor parafollicular cells expressed NCAM at detectable levels. All papillary carcinomas and most poorly differentiated follicular carcinomas and some follicular adenomas demonstrated NCAM expression. In thyroid carcinoma, clinical stage and recurrent laryngeal nerve paralysis did not correlate significantly with expression of NCAM. Papillary carcinomas with strong expression of NCAM were more likely to have extra capsular invasion. It is supposed that immunohistochemical detection of NCAM expression supports histologic diagnosis and offers prognostic information.