The thyroid gland, from the Greek words thyreos (shield) and eidos(shape) is one of the largest endocrine organs, with a remarkable potential for growth and enlargement. Diseases due to altered parenchymal function and anatomic abnormalities of this gland are among the most common endocrine disorders in humans. Thyroid carcinoma is the most common endocrine malignancy, and both non neoplastic and neoplastic abnormalities are a frequent source of specimens for surgical pathology laboratories. Thyroid nodules are highly prevalent and often require cytopathologic evaluation. The general theme is that of the “needle in the haystack”: many are the thyroid nodules, few are those with malignant potential; of the malignant tumors, few are those that pose a significant threat for the patient life – although some of them, like anaplastic carcinoma, are among the most aggressive forms of human cancer. While most thyroid tumors are sporadic, a few develop in a familial setting or in the context of well-defined tumor syndromes (medullary carcinoma and MEN2 being the prototypical examples for C-cells, follicular carcinoma and Cowden syndrome for follicular cells). Some thyroid lesions pose considerable diagnostic challenges, and Dr. J. Rosai used to quote the words of the famous French pathologist C. L. Pierre Masson (one of the fathers of surgical pathology): “Of all cancers, thyroid epitheliomas teach, perhaps, the greatest lesson of humility to histopathologists”. Ancillary techniques, including immunohistochemistry and molecular diagnostics, may help resolve these difficult cases. What follows is an account of the relevant topics in the routine surgical pathology practice of the thyroid gland