Genetic testing and the consequent clinical management in multiple endocrine neoplasia type 2 (MEN 2) represent an important paradigm for the practice of molecular oncology. MEN 2 is a relatively rare autosomal dominant inherited neoplasia syndrome characterized by medullary thyroid carcinoma (MTC), phaeochromocytoma (PC) and hyperparathyroidism (HPT) (reviewed in Ponder1
and Eng2). Germline mutations in only one susceptibility gene, RET localized to 10q11.2, are responsible for 95 per cent of all MEN 2.3 Because of the single susceptibility gene, the limited number of mutations involved and the high frequency of mutations in MEN 2, sensitivity, the specificity and cost effectiveness of RET mutation analysis are high. The accuracy of the test and the ability of such results to alter medical management have made RET mutation testing part of the routine clinical care of patients with known MEN 2, suspected MEN 2 and, in some countries, all isol-ated presentations of MTC.