Among various substances produced by C-cells, the most important one is calcitonin (CT) that is used for detection, postoperative follow-up and evaluation of individuals at risk of developing medullary thyroid carcinoma (MTC). However, the role of serum CT measurement in the evaluation of thyroid nodules has been widely discussed, and there is still no consensus about the role of CT in the initial evaluation of all thyroid nodules. Two patients with thyroid nodules whose fine-needle aspiration results were compatible with benign cytology besides having mildly elevated basal serum calcitonin levels were reported. Calcitonin responses (peak levels were 313 and 229 pg/mL, respectively) to calcium stimulation test were compatible with the possible diagnosis of MTC. However, the final diagnosis was papillary thyroid carcinoma of the thyroid gland. There are limited numbers of case reports showing such an increased serum calcitonin responses to calcium stimulation test associated with papillary or follicular thyroid carcinoma of the thyroid. We suggest to measure serum CT level once and in case of normal levels, no further CT measurement is necessary. Physicians should keep in mind that thyroid carcinomas other than MTCs may also be associated with high serum CT levels.