Despite the low incidence of thyroid carcinoma this heterogenic group of tumors is the most common malignant endocrine disease. The spectrum of virulence in thyroid cancer ranges from a rather indolent course with almost normal survival rates to the most lethal, undifferentiated tumor with survival rates of only few weeks or months. Advances in diagnosis and therapy especially of hereditary medullary carcinoma have been made based on identification of the genetic defect causing the occurrence of this tumor. The key in therapy of thyroid carcinoma is in most of the cases the resection of the thyroid gland.