Medullary thyroid carcinoma (MTC) originates in the parafollicular neuroendocrine cells of the thyroid. In 25% of cases, MTC is a component of the type 2 multiple endocrine neoplasia (MEN) syndromes, MEN2A and MEN2B. MEN2 originates from mutations in the RET protooncogene, for which more than 100 mutations have been described. There is a high genotype-phenotype correlation, which allows to determine the frequency and time of occurrence of the different clinical manifestations of MEN2 (mainly MTC, pheochromocytoma and primary hyperparathyroidism). The combination of genetic knowledge and clinical elements, such as the concentration of serum calcitonin, has allowed the development of recommendations regarding the timing of prophylactic thyroidectomy. The objective of prophylactic thyroidectomy is to remove the thyroid before MTC develops, or while it is confined to the gland, thus avoiding the morbidity and mortality associated with this neoplasm. This review describes the characteristics of hereditary MTC, presents the knowledge considered to develop the recommendations for prophylactic thyroidectomy, and summarizes the studies that have evaluated the effectiveness of this intervention.