Medullary thyroid cancer (MTC) is a rare disease with a highmortality. Otherwise, the advances in diagnosesmethod andtreatment had permit better outcomes, mainly, afterintroduction of RET proto-oncogene test in the investigation ofmutations and the possibility of prophylactic thyroidectomyindication. The aim of this study is to present a case report of apatient with RET proto-oncogenemutationwho underwent aprophylactic thyroidectomy and confirm MTC.(AU)