Medullary Thyroid Carcinoma is a rare thyroid tumororiginating from neural crest cells, the C-cell that impliesseveral special features, secretion of differentneuroendocrine markers, association with other endocrinetumors and familial appearance. The familial variant ofmedullary thyroid carcinoma allows an early detection bybiochemical and genetic testing. At that stage acceptablesurgical treatment will cure the patient. The sporadic formof medullary thyroid carcinoma will be diagnosed in aprogressive stage, but adequate surgical procedure can curethese patients too. Long term survival depends on stage,age, sex, and variant of the disease and seems to be as goodas in other differentiated thyroid cancers.Medullary Thyroid Carcinoma is a rare thyroid tumororiginating from neural crest cells, the C-cell that impliesseveral special features, secretion of differentneuroendocrine markers, association with other endocrinetumors and familial appearance. The familial variant ofmedullary thyroid carcinoma allows an early detection bybiochemical and genetic testing. At that stage acceptablesurgical treatment will cure the patient. The sporadic formof medullary thyroid carcinoma will be diagnosed in aprogressive stage, but adequate surgical procedure can curethese patients too. Long term survival depends on stage,age, sex, and variant of the disease and seems to be as goodas in other differentiated thyroid cancers.Biological Aspects of Medullary Thyroid Carcinoma.- Regulation of Calcitonin Secretion and Calcitonin Gene Expression.- Pathology of Sporadic and Hereditary Medullary Thyroid Carcinoma.- Epidemiology of Medullary Thyroid Carcinoma.- Clinical and Diagnostic Aspects of Medullary Thyroid Carcinoma.- Tumor Markers for the Medullary Thyroid Carcinoma.- Sporadic Medullary Thyroid Carcinoma: Clinical Features and Diagnosis.- Screening for MEN 2 with Biochemicall6