We conducted a large-scale nationwide questionnaire survey to characterize the clinical course of inherited medullary thyroid carcinoma (MTC). Out of a total of 634 MTC patients (M:F ratio 1:2.5), 175 patients had multiple endocrine neoplasia (MEN) 2A, 49 had familial non-MEN medullary thyroid carcinoma (FMTC), 20 had MEN 2B, and 390 had sporadic MTC. Median age at the time of diagnosis was 40.3, 43.0, 26.5 and 48.5 years, respectively. Total thyroidectomy plus modified neck dissection (MND) was the most common operation. The 5-year survival rates were 96.9% in MEN 2A, 100% in FMTC, 73.8% in MEN 2B, 90.8% in sporadic MTC. The outcome in order from best to worst was: FMTC, MEN 2A, sporadic MTC, and MEN 2B, with MEN 2B considered the most aggressive type.