Epithelial-mesenchymal transitions (EMT) are essential for normal embryonic development and for progression of non-invasive tumor cells into metastatic carcinomas. During embryogenesis, the parathyroid glands develop from pharyngeal pouches and migrate to their final destinations, densely enclosed by mesenchymal neural crest cells. We compared expression of E-cadherin, Snail and Twist in patients with parathyroid adenoma, hyperplasia, and parathyroid cancer with normal glands. In normal parathyroid glands, adenomas and hyperplasias, E-cadherin showed a typical membranous staining pattern, and Snail and Twist positive cells were homogeneously distributed in almost all glands. In all nine parathyroid carcinomas, membranous E-cadherin staining was lost. In addition, the expression pattern of Snail and Twist changed, and was mostly limited to the invasive front of cancer tissue samples. Expression of Snail and Twist at the invasive front and consecutive loss of E-cadherin in parathyroid carcinomas suggests a key role of EMT in the tumorigenesis of this cancer. The unique expression pattern could help to distinguish between an adenoma and a non-metastatic carcinoma.