Medullary thyroid carcinoma (MTC) occurs sporadically or as an inherited disease, with the latter occurring in the form of multiple endocrine neoplasia (MEN) type 2A, MEN type 2B, or familial non-MEN medullary carcinoma (FMTC). MTC is inherited as an autosomal dominant trait and is associated with germline mutations of the RET proto-oncogene. Genetic testing identifies carriers of the mutant gene and enables preventive thyroidectomy. A nationwide questionnaire-based survey was conducted in 1996 and again in 2002, and we report here the results of the two surveys that characterize the clinical course of the inherited form of MTC. The data show a higher rate of inherited MTC than previously described, although MEN2A was found to be the most common inherited form of MTC, the same as in earlier studies. The most important finding was the difference in method of detection of MTC between the two surveys. Since the discovery of the genetic association with the disease, genetic testing has become the diagnostic method of choice, replacing indicators such as neck mass and elevated non-stimulated serum calcitonin level. Genetic testing enables early detection of the disease, which provides patients with the possibility of better outcome.