Thyroid incidentaloma is a common disorder in endocrinology practice. Current literature regarding the risk of thyroid cancer in incidentalomas found in patients with non-thyroid cancer is limited. The aim of the present study was to investigate the frequency of thyroid malignancy in thyroid incidentalomas detected in patients with non-thyroid cancer. Case control study. The database of 287 thyroid nodules from 161 patients with a history of non-thyroid cancer followed between 2008 and 2014 were retrospectively evaluated. From 287 thyroid nodules, 69.7 % had a benign final cytology. Thyroid cancer detected in one nodule while follicular neoplasia detected in 4 nodules, atypia of unknown significance (AUS) detected in 10 nodules, Hurthle cell neoplasia detected in 5 nodules and suspicious for malignancy detected in 6 nodules according to fine needle aspiration biopsy results. Metastasis of the non-thyroid cancer to the thyroid gland was detected in 4 nodules. Twenty seven nodules from 15 patients were removed with surgery. There were 3 malignant nodules found after surgery (1 papillary, 1 follicular and 1 medullary cancer). In addition to these three thyroid cancers, two patients with benign nodules had co-incidental thyroid cancer detected after surgery. Finally, 11.1 % of thyroid nodules which underwent thyroid surgery had malignant histopathology except for co-incidental and metastatic cancers. The frequency of thyroid malignancy seems not to be substantially increased in incidental thyroid nodules detected in patients with non-thyroid cancer when these patients were evaluated in nodule-based approach.