Introduction: Thyroid carcinoma including into four types papillary, follicular, medullary, and anaplastic is the most common endocrine malignancy. Medullary thyroid carcinoma (MTC) is one of the most aggressive forms of thyroid cancer and it accounts for up to 10% of all types of this disease. The mode of inheritance of MTC is autosomal dominant and is closely related to mutations of gain of function (missense mutations) in the RET proto-oncogene, well known in MTC development. MTC occurs as hereditary (25%) and sporadic (75%) forms. Hereditary MTC also has two syndromic (multiple endocrine neoplasia type 2A, B MEN2A, MEN2B) and non-syndromic (Familial MTC, FMTC) types. Increasing advances in molecular biology, genomics, and proteomics have led to personalized therapeutic interventions. Over the last two decades, the genetic basis of tumorgenesis has provided useful screening tools for affected families. Advances in genetic screening of the RET have enabled early detection of hereditary MTCs and prophylactic thyroidectomy for relatives who may not show any symptom of the disease. In this review we emphasize the main RET mutations in the syndromic and non syndromic forms of MTC, and have tried focus on the importance of RET genetic screening for early diagnosis and management of MTC patients.