OBJECTIVE: The prognosis of medullary thyroid carcinoma (MTC), derived from parafollicular C-cells, depends on the completeness of the initial surgical excision. The C-cells produce calcitonin, a peptide hormone used as a biochemical and immunohistochemical tumor marker. The aim of the study was to evaluate an individualized approach to patients with C-cell disease, i.e. MTC and C-cell hyperplasia (CCH), using the intraoperative calcitonin testing-assisted surgical strategy as a predictor of the final outcome. STUDY DESIGN: A unicentre cross-sectional study. METHODS: From June 2009 to May 2015, thirty one patients with MTC/CCH were surgically treated primarily (n=24) or reoperated for persistence of the disease (n=7). Depending on the result of intraoperative calcitonin stimulation testing (iCST), patients underwent total thyroidectomy with or without lymph node dissection. All patients were tested repeatedly in the postoperative period (range 1 to 48 months). RESULTS: The iCST was true negative in all CCH, and ten out of eleven N0 MTC primarily operated patients, and true positive in one N0 patient and six of the seven reoperated patients. The test was false negative in two patients preoperatively evaluated as N+, one primarily operated and one reoperated, respectively. CONCLUSION: The results encourage the use of an individualised approach on patients with MTC/CCH, e.g. to be less radical surgically in cases of negative iCST, and to be more radical in those patients with persistent increase of serum calcitonin. The absence of post-stimulation calcitonin elevation in iCST seems to be a good prognosis indicator in patients with an early-stage C-cell disease, but longer follow-up is needed.