['Medullary thyroid carcinoma is a rare tumour derived from the thyroid parafollicular calcitonin-secreting cells. Calcitonin is a very specific marker of this cancer that allows preoperative diagnosis. Serum calcitonin assay is particularly useful to define the postoperative state of patients (cured, apparently cured, not cured) and, because of its great sensitivity, it has a major place in the postoperative follow-up.', 'To identify, among patients thyroidectomized for medullary thyroid carcinoma (MTC), the characteristics of authentic recurrent MTC [re-elevation of stimulated serum calcitonin (CT) level measured by a sensitive immunoradiometric assay, after postoperative normalization].', 'We first collected, through the national registry of the French Calcitonin Tumour Study Group (GETC), patients who had undergone a total thyroidectomy with or without lymph node surgery and who were not cured at the last follow-up visit. Among 453 such patients included in the database, 15 patients met the criteria for authentic recurrence as defined in previous studies: they had been first considered as cured during the 6 months following the initial surgical procedure (basal and pentagastrin-stimulated serum calcitonin level <or= 10 ng/l) but had a secondary rerise of their pentagastrin-stimulated calcitonin level, over 10 ng/l. Eight of them even had an undetectable (< 2 ng/l) immediate postoperative CT, confirming the initial postoperative cure. The characteristics (age, nature of disease, stage at surgery and type of node dissection) of these 15 patients were studied.', 'According to the Tumour Node Metastasis classification, nine patients were T1 and, among them, five patients had had complete lymph node surgery without any evidence of nodal metastases (N0). The recurrence was 3.2 +/- 2.2 years (range: 0.7-7.5) after the initial surgery.'] Does complete surgical lymph node resection prevent authentic recurrences of medullary thyroid carcinoma?