Most cases of medullary thyroid carcinomas (MTC) are sporadic. But 25% occur in inherited syndromes such as familial medullary thyroid cancer and MEN types 2A and 2B. These occur due to germline mutations in the RET protooncogene. MEN2A consists of Medullary thyroid cancer, Pheochromocytoma and Primary hyperparathyroidism. MEN 2B consists of MTC, Pheochromocytoma, Mucosal neuromas, Gangliomas, and aMarfan-like habitus. Any patient with MEN 2A or MEN 2B may develop medullary carcinoma at a very young age and therefore should be followed carefully for pheochromocytoma with urine VMA, for hyperparathyroidism with serum calcium, and for medullary carcinoma with serum calcitonin.