These NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) focus on medullary thyroid carcinoma (MTC). NCCN Guidelines addressing papillarc follicular, HOrthle cell, and anaplastic thyroid carcinomas will appear in a later issue of JNCCN. Sporadic MTC accounts for approximately 80% of all cases of the disease. Sporadic disease typically presents in the fifth or sixth decade. Familial forms of the disease tend to present at earlier ages. Because the C cells are predominantly located in the upper portion of each thyroid lobe, patients with sporadic disease typically present with upper pole thyroid nodules. Metastatic cervical adenopathy appears in approximately 50% of patients at initial presentation. Symptoms of upper aerodigestive tract compression or invasion are reported by up to 15% of patients with sporadic disease. Symptoms from distant metastases in lungs or bones occur in 5% to 10% of patients. The risk for concomitant or subsequent development of pheochromocytoma and hyperparathyroidism must always be considered. © Journal of the National Comprehensive Cancer Network.