The heredity of medullary thyroid carcinoma within the MEN2 syndrome is caused by heterozygous germline mutations in the RET protooncogene. Since the MEN2-associated mutations involve only hot spots, molecular genetic analysis of the RET proto-oncogene is the perfect tool for diagnosis of MEN2 and is considered the standard method. Molecular genetic screening for MEN2-associated RET germline mutations should be initiated in all patients with an apparently sporadic medullary thyroid carcinoma or pheochromocytoma. This testing has to include exons 10, 11, and 13-16 of the RET proto-oncogene. The investigation is aimed at identifying an index person of a new MEN2 family. The detection of such a RET germline mutation is the basis for the predictive molecular genetic testing within the affected family and results in the exclusion or identification of gene carriers. For these persons at risk, prophylactic total thyroidectomy is recommended as a curative procedure according to a risk-adapted genetically based algorithm of treatment. The care of such affected families should be accompanied by oncological and genetic counseling.