BACKGROUND AND AIMS The administration of Liraglutide, a long-acting GLP-1 receptor (GLP-1R) agonist, is associated with C-cell adenomas and carcinomas in rats. In humans, GLP-1R is highly expressed in C-cells hyperplasia (CCH) and in medullary thyroid cancer (MTC), though no changes in basal serum calcitonin (bCT) levels were recorded in type 2 diabetic (T2DM) patients treated with Liraglutide. To diagnose the possible development of CCH during Liraglutide treatment, we evaluated CT levels stimulated by calcium test (sCT). MATERIALS AND METHODS bCT and sCT and metabolic and anthropometric parameters were evaluated in 26 T2DM patients at baseline and at 1, 3, 6 and 12 months of treatment. RESULTS In all patients, bCT remained within the normal range during the entire study period. In females and males, the higher sCT values were reached after 3 months and 1 month, respectively, with a progressive reduction at 6-12 months. The greater decrease of HbA1c values was reached at 3 months, while body weight and waist circumference decreased over the first 4 weeks of therapy. Lipase levels significantly increased, with a peak value at 1 month. CONCLUSION The chronic administration of Liraglutide did not lead to statistically significant variations in both bCT and sCT. Stimulated CT levels increased, though always below the normal range, during the first 1-3 months of treatment, and progressively decreased to baseline levels. This finding is consistent with the effects recorded at the glycometabolic level, and suggests the possible induction of a drug tolerance involving also the C cells and thus preventing CCH.