Thyroid carcinomas represent the most common endocrine malignancy, and several biological markers are proposed according to the different types of this cancer: for papillary cancer, thyroglobulin constitutes an excellent prognostic factor and rearrangements of ret oncogene can be useful in diagnosis. In sporadic medullary carcinoma, calcitonin is a diagnosis marker of choice, and coupled with ACE, can prevent relapse. Regarding familial medullary carcinoma, mutation screening in ret oncogene leads to early detection of new cases.